Other  works  by  same  author 
in  collaboration  with 

PROF.  SAMUEL  SHELDON 


DYNAMO  ELECTRIC  MACHINERY;   its 

Construction,  Design  and  Operation 
VOL.  I.  DIRECT  CURRENT  MACHINES 

Eighth  Edition  completely  re -written , 
5^x7|<  Cloth  338  Pages,  Illustrated  Net  $2.50 

VOL.  II.  ALTERNATING  CURRENT 

MACHINES,  Tenth  Edition  revised, 
$}4x7%  Cloth  366  Pages,  Illustrated  Net  $2.50 


ELECTRIC  TRACTION  AND  TRANSMIS- 
SION ENGINEERING 

5^x7^  Cloth  318  Pages,  Illustrated  Net  $2.50 


Telegraph  Engineering 

A    MANUAL    FOR    PRACTICING   TELEGRAPH 

ENGINEERS    AND    ENGINEERING 

STUDENTS 


BY 

ERICH    HAUSMANN,    E.  E.,  Sc.  D. 

%  • 

Assistant  Professor  of  Physics  and  Electrical  Engineering 

at  the  Polytechnic  Institute  of  Brooklyn,  and 

Member  of  the  American  Institute 

of  Electrical  Engineers. 


WITH  192  ILLUSTRATIONS 


NEW   YORK 

D.   VAN    NOSTRAND    COMPANY 

25  PARK  PLACE 

1915 


COPYRIGHT,  1915, 

BY 
D.  VAN  NOSTRAND  COMPANY 


Stanbopc  ipress 

F.    H.  GILSON   COMPANY 
BOSTON,  U.S.A. 


DEDICATED  To 

Sorter  8>amu? 

IN   APPRECIATION    OF   HIS   INSPIRING   INFLUENCE 


PREFACE 


THIS  book  is  intended  for  electrical  engineering  students 
and  as  a  reference  book  for  practicing  telegraph  and  tele- 
phone engineers  and  for  others  engaged  in  the  arts  of  elec- 
trical communication.  It  presents  in  a  logical  manner  the 
subject  of  modern  overland  and  submarine  telegraphy 
from  an  engineering  viewpoint,  its  theoretical  and  practical 
aspects  being  correlated.  No  attempt  is  made  to  describe 
all  telegraphic  devices  and  to  explain  their  operation,  but 
rather  to  consider  one  or  more  representative  types  for  the 
accomplishment  of  the  various  desired  objects,  thus  per- 
mitting a  presentation  of  the  subject  matter  in  proper  per- 
spective. The  book  is  the  outgrowth  of  the  course  in 
Telegraph  Engineering  given  by  the  author  for  a  number 
of  years  at  the  Polytechnic  Institute  of  Brooklyn. 

A  knowledge  of  elementary  electricity  and  magnetism 
is  presupposed.  For  understanding  the  mathematical 
demonstrations  a  knowledge  of  algebra  will  in  many  cases 
suffice,  but  in  other  cases,  appearing  toward  the  latter  part 
of  the  book,  the  calculus  is  a  necessary  adjunct,  the  study 
of  which  frequently  precedes  or  accompanies  the  vocational 
studies  of  students  and  progressive  telegraph  workers. 
That  the  use  of  higher  mathematics  is  important  in  the 
thorough  pursuit  of  telegraph  and  telephone  transmission 
studies  is  evident  from  an  inspection  of  the  writings  of 
Lord  Kelvin,  Heaviside,  Kennelly,  Pupin,  Campbell,  Mal- 
colm and  others.  Those  not  versed  in  mathematical 

vii 


Viii  PREFACE 

processes,  however,  may  yet  share  in  the  value  of  the 
demonstrations  by  an  analysis  of  their  conclusions  and  an 
examination  of  the  numerical  illustrations  based  upon  them. 
The  solution  of  practical  problems  appended  to  each  chap- 
ter will  assist  in  a  complete  understanding  of  the  principles 
presented. 

The  author  expresses  his  appreciation  and  thanks  to  Mr. 
Herbert  W.  Drake,  Apparatus  Engineer  of  the  Western 
Union  Telegraph  Company,  for  making  helpful  suggestions 
and  for  reading  the  page  proofs  of  the  first  six  chapters. 
He  also  gratefully  acknowledges  the  inspiration  and  en- 
couragement in  the  preparation  of  this  work  derived  from 
his  intimate  association  with  Dr.  Samuel  Sheldon,  Professor 
of  Physics  and  Electrical  Engineering  at  the  Polytechnic 
Institute  of  Brooklyn. 

E.  H. 

BROOKLYN,  N.  Y. 
January,  1915. 


CONTENTS 


CHAPTER  I. 
SIMPLEX  TELEGRAPHY. 

ART.  PAGE 

1.  Simplex  Signalling i 

2.  The  Use  of  Relays 3 

3.  Closed-  and  Open-circuit  Morse  Systems 5 

4.  Telegraph  Instruments 8 

5.  Best  Winding  for  Receiving  Instruments 16 

6.  Sources  of  Current 20 

7.  Telegraph  Codes 25 

8.  Telegraph  Lines 28 

9.  Speed  of  Signalling 33 

10.   Simplex  Repeaters 35 

Problems 43 

CHAPTER  II. 
DUPLEX  TELEGRAPHY. 

r.  Duplex  Telegraph  Systems 45 

2.  The  Differential  Duplex 46 

3.  Artificial  Lines 51 

4.  Polarized  Relays 53 

5.  The  Polar  Duplex 56 

6.  Improved  Polar  Duplex 63 

7.  Short-line  Duplex 66 

8.  The  Bridge  Duplex 67 

9.  Advantage  of  Double-current  Duplex  Systems 74 

10.  Duplex  Repeaters 76 

11.  Half-set  Repeaters 80 

Problems , 83 

CHAPTER  III. 
QUADRUPLEX  TELEGRAPHY. 

1.  Quadruplex  Systems 85 

2.  Operation  of  Quadruplex  Systems 87 

3.  Avoidance  of  Sounder-armature  Release  during  Current  Rever- 

sals in  Neutral  Relay 94 

ix 


X  CONTENTS 

ART.  PAGE 

4.  The  Postal  Quadruplex 96 

5.  The  Western  Union  Quadruplex 98 

6.  Quadruplex  Repeaters 100 

7.  Duplex-diplex  Signalling 102 

,  8.  Phantoplex  System 103 

Problems 106 

CHAPTER  IV. 
AUTOMATIC  AND  PRINTING  TELEGRAPHY. 

1.  Wheatstone  Automatic  Telegraphy 108 

2.  Ticker  Telegraphs. 115 

3.  The  Barclay  Page-printing  Telegraph  System 121 

4.  Other  Printing  Telegraph  Systems 133 

Problems 134 

CHAPTER  V. 
TELEGRAPH  OFFICE  EQUIPMENT  AND  TELEGRAPH  TRAFFIC. 

1.  Protective  Devices 135 

2.  Peg  Switch  Panels 136 

3.  Main  and  Loop  Switchboards 138 

4.  Distributing  Frames 143 

5.  Instrument  Tables 145 

6.  Power  Switchboards 146 

Traffic. 

7.  Types  of  Messages 150 

8.  Classes  of  Service  and  Tariffs 152 

9.  Handling  of  Traffic 154 

10.  The  Telegraph  in  Railway  Operation 157 

n.  Telegraph  Statistics 159 

Problems 161 

CHAPTER  VI. 

MISCELLANEOUS  TELEGRAPHS. 

1.  Multiplex  Telegraph  Systems 162 

2.  The  Murray  Multiplex  Page-printing  Telegraph 163 

3.  The  Pollak-Virag  Writing  Telegraph 167 

4.  The  Telautograph 170 

5.  Telephotography 175 


CONTENTS  xi 

ART-  PAGE 

6.  Television j82 

7.  Military  Induction  Telegraphs 184 

Problems !88 

CHAPTER  VII. 

MUNICIPAL  TELEGRAPHS. 

1.  Fire-alarm  Telegraphy X8g 

2.  Fire-alarm  Signal  Boxes 192 

3.  Public  Alarms 200 

4.  Fire-alarm  Central  Stations 202 

5.  Signalling  Devices  at  Apparatus  Houses 210 

6.  Operation  and  Routine  of  a  Fire-alarm  Telegraph  System 212 

7.  Police  Patrol  Telegraphs 217 

8.  Statistics  of  Police  and  Fire  Signalling  Systems 221 

Problems 223 

CHAPTER  VIII. 
RAILWAY  SIGNAL  SYSTEMS. 

1.  Classes  of  Railway  Signalling 224 

2.  Types  of  Signals 225 

3.  Manual  Block  Signal  Systems 231 

4.  Location  of  Automatic  Block  Signals 232 

5.  Automatic  Block  Signalling 237 

6.  Automatic  Block  Signals  on  Electric  Railways 242 

7.  Interlocking  Plant  Signals 247 

Problems 251 

CHAPTER  IX. 
TELEGRAPH  LINES  AND  CABLES. 

1.  Aerial  Open  Lines 253 

2.  Wire  Spans 261 

3.  Economical  Span  Length - 266 

4.  Telegraph  Cables 269 

5.  Underground  Cable  Installation 273 

6.  The  Earth  as  a  Return  Path 279 

7.  Electrical  Constants  of  Telegraph  Conductors 282 

8.  Elimination  of  Inductive  Interferences  on  Telegraph  and  Tele- 

phone Lines 288 

9.  Simultaneous  Use  of  Lines  for  Telegraphy  and  Telephony 293 

Problems 300 


Xli  CONTENTS 

CHAPTER  X. 

« 

THEORY  OF  CURRENT  PROPAGATION  IN  LINE  CONDUCTORS. 

ART.  PAGE 

1.  The  Transmission  of  Current  Impulses  along  Telegraph  Lines.  . .  303 

2.  Propagation  of  Alternating  Currents  along  Uniform  Conductors 

of  Infinite  Length 306 

3.  Velocity  of  Wave  Propagation  over  an  Ideal  Line 313 

4.  Wave  Propagation  along  Conductors  of  Finite  Length 314 

5.  Simplified  Equations  of  Wave  Propagation 321 

6.  Current  and  Voltage  Distribution  on  Lines  for  any  Terminal  Con- 

dition    324 

7.  Effect  of  Impedance  at  Sending  End 328 

8.  Illustration  of  Sine-wave  Telegraphic  Transmission 330 

9.  Current  in  Leaky  Line  Conductors 334 

10.  Illustration  of  Direct-current  Signalling  on  a  Leaky  Telegraph 

Line 338 

11.  Simplex  Signalling  with  Generators  at  Both  Line  Terminals 341 

12.  Duplex  and  Quadruplex  Signalling 344 

Problems 346 

CHAPTER  XL 
SUBMARINE  TELEGRAPHY. 

1.  Theory  of  Cable  Telegraphy 347 

2.  Illustration  of  Current  Growth  at  the  Receiving  End  of  a  Cable.  354 

3.  Transmission  of  Telegraphic  Signals 355 

4.  Speed  of  Signalling 363 

5.  Picard  Method  of  Signalling 367 

6.  Gott  Method  of  Signalling 369 

7.  Duplex  Cable  Telegraphy 372 

8.  Sine-wave  Signalling 374 

9.  Design  of  Submarine  Cables 375 

10.  Types  of  Cable  Service  and  Tariffs 381 

Problems. 385 

APPENDIX. 
TABLES. 

I.  Trigonometric  Functions 388 

II.   Exponential  Functions 39° 

III.  Logarithms 392 

IV.  Hyperbolic  Functions 394 


TELEGRAPH  ENGINEERING 


CHAPTER   I 

SIMPLEX  TELEGRAPHY 

i.  Simplex  Signalling.  —  The  transmission  of  intelligence 
between  two  points  by  means  of  electricity  was  accom- 
plished in  1837  by  Professor  Samuel  F.  B.  Morse  of  New 
York  University.*  Seven  years  later  he  constructed  the 
first  telegraph  line  in  this  country  (Baltimore  to  Washing- 
ton). The  modernized  system  comprises  a  conveniently- 
operated  switch  called  a  key,  for  opening  and  closing  the 
circuit  at  one  place,  a  source  of  electric  current,  an  electro- 
magnetic receiving  device  capable  of  producing  an  audible 
effect,  called  a  sounder,  at  another  place,  and  a  line  wire  con- 
necting the  two  places  or  stations.  Signals  are  transmitted 
over  such  a  circuit  by  opening  and  closing  the  circuit  by 
means  of  the  key  for  long  and  short  intervals  in  ac- 
cordance with  a  prearranged  code,  and  are  interpreted 
at  the  other  station  by  the  sounds  produced  by  the  move- 
ments of  a  pivoted  spring-controlled  lever  actuated  by  an 
electromagnet  which  is  traversed  by  the  current  pulses 
established  by  the  key.  In  order  to  transmit  messages  in 
either  direction,  the  apparatus  mentioned  is  duplicated 
and  connected  with  the  single  line  wire  as  shown  in  Fig.  i. 

The  earth  is  generally  utilized  as  the  return  path  for  the 

*  Earlier  electric  telegraphs  are  described  in  J.  J.  Fahie's  "  A  History  of 
Electric  Telegraphy  to  1837." 


2 


TELEGRAPH  ENGINEERING 


current,  thereby  saving  the  expense  of  another  line  wire 
and  also  avoiding  the  additional  resistance  introduced 
thereby.  The  resistance  of  the  ground-return  path  GG  is 
negligible  in  comparison  with  the  resistance  of  the  line  wire, 
for  in  nearly  all  cases  it  is  less  than  one  ohm.  This  low 
resistance  is  due  to  the  enormous  cross-sectional  area  of  the 
earth  path,  although  the  conductivity  of  the  earth's  crust  is 
poor.  Recent  experiments,  made  by  Lowy,  indicate  that 
the  specific  resistance  of  a  variety  of  rocks  is  greater  than 
io5  ohms  per  centimeter  cube,  depending  upon  the  amount 
of  moisture  in  them.  To  attain  low  earth  resistances  it  is 


=rB 


—  G 

Fig.  i. 

essential  that  good  connections  be  made  between  the  line 
wire  and  earth,  by  iron  pipes  driven  in  damp  ground  or 
more  usually  by  attachment  to  municipal  water  pipes. 

When  the  line  is  idle  the  circuit  of  Fig.  i  is  kept  closed 
by  means  of  the  circuit-closing  switches  s,  5  in  parallel  with 
the  keys  K,  K,  causing  a  current  to  flow  continually  from 
ground  G  at  station  A  through  switch  s,  battery  (or 
generator)  B,  sounder  S,  line  L,  sounder  5,  battery  (or 
generator)  By  and  switch  5  to  ground  G  at  station  B.  When 
the  operator  at  station  A  wishes  to  send  messages,  he 
interrupts  the  current  by  opening  his  circuit-closer  s  (as 


SIMPLEX  TELEGRAPHY  3 

shown  in  Fig.  i)  and  then  establishes  current  pulses  by 
depressing  his  key  for  long  or  short  intervals  producing 
respectively  so-called  dashes  and  dots,  various  combi- 
nations of  which  constitute  the  letters  and  numbers  of  a 
code.  These  current  pulses  flow  through  the  windings  of 
both  sounders,  causing  the  armatures  on  the  levers  to  be 
attracted  and  released  repeatedly  and  causing  the  other 
ends  of  these  levers  to  strike  against  lower  and  upper 
stops,  /  and  u.  The  long  and  short  intervals  between  the 
two  different  sounds  produced  by  striking  the  lower  and 
upper  stops  are  translated  by  ear  as  dashes  and  dots  by 
both  operators.  The  sending  operator  therefore  hears  his 
own  message  and  is  enabled  to  detect  possible  errors;  it 
also  serves  as  an  indication  that  the  line  is  not  open-cir- 
cuited. When  the  operator  is  through  sending  signals,  he 
again  completes  the  circuit  by  means  of  the  circuit-closer, 
thereby  enabling  the  other  operator  to  answer. 

The  system  described  permits  of  signalling  in  only  one 
direction  at  a  time,  and  is  therefore  called  a  single  Morse, 
or  conveniently,  a  simplex  telegraph  system.  It  is  still  in 
use  at  present  for  short  distances,  and  with  more  sensitive 
receiving  instruments  may  be  used  for  longer  distances. 

2.  The  Use  of  Relays.  —  The  lever  of  a  sounder  must 
have  a  certain  mass  so  as  to  produce  loud  and  distinct 
sounds  when  striking  the  stops.  A  definite  magnetizing 
force  is  required  to  move  the  lever  with  positiveness  in 
opposition  to  its  adjustable  retractile  spring.  This  mag- 
netizing force  is  measured  by  the  product  of  the  number  of 
turns  of  wire  on  the  sounder  winding  and  the  current 
traversing  it.  Sounders  of  the  usual  construction  require 
from  150  to  500  ampere- turns  for  proper  operation. 


4  TELEGRAPH  ENGINEERING 

On  long  lines  having  high  resistance  the  current  is 
necessarily  small  for  practicable  voltages,  and  it  would  not 
be  feasible  to  use  ordinary  sounders  wound  with  a  great 
many  turns  of  fine  wire  to  secure  a  proper  magnetizing  force 
because  of  the  additional  resistance  introduced.  Instead, 
more  sensitive  instruments,  called  relays,  are  used,  which 
have  light  armatures  with  contact  points  that  open  and 
close  local  circuits  containing  sounders  and  local  batteries. 
Such  relays  for  simplex  signalling  require  a  magnetizing 
force  of  from  70  to  300  ampere-turns. 

For  a  given  impressed  voltage  E  on  a  perfectly  insulated 
ground-return  line  of  length  /  miles,  having  a  resistance  of 
R  ohms  per  mile,  with  two  receiving  instruments  each  of 
Rr  ohms  resistance,  the  steady  current  in  the  circuit  is 


If  7min  be  the  minimum  current  which  will  actuate  the 
receiver,  the  limit  of  transmission  for  a  given  voltage  E  is 

(i) 

If  the  electromotive  force  E  be  developed  by  Nb  series- 
connected  primary  batteries,  each  of  voltage  e  and  internal 
resistance  Rb,  then  replace  E  in  the  foregoing  equations  by 


Thus,  if  two  2o-ohm  sounders  requiring  a  current  of 
•5-  ampere  be  the  receiving  instruments  on  a  i2.4-ohm-per- 
mile  ground-return  line,  the  maximum  length  of  line 
operated  on  140  volts  would  be 


I2.4\0.20 


_  2  x  20 


)  =  52  miles; 

/ 


SIMPLEX  TELEGRAPHY 


whereas  if  i5o-ohm  relays  requiring  a  current  of  0.04 
ampere  be  the  receiving  instruments,  the  distance  of  trans- 
mission over  this  line  would  be 


12.4 


-  2  X  150 


J=  258  miles, 


a  distance  five  times  as  great  as  before.  By  the  use  of 
lines  of  lower  resistance  per  unit  length,  the  distance  of 
transmission  can  be  increased  in  both  cases. 

The  voltage  necessary  for  telegraphic  transmission  over 
a  given  distance  can  also  be  found  from  equation  (i). 
Voltages  over  200  are  rarely  employed  in  simplex  signalling. 

The  windings  of  relays  and  sounders  are  generally  des- 
ignated by  their  resistance  although  the  number  of  turns 
is  the  important  consideration;  this  is  done  because  of  the 
ease  in  measuring  the  resistance  of  a  finished  instrument. 

3.   Closed-    and    Open-circuit   Morse    Systems.  —  The 

simple  Morse  circuit  of  Fig.  i  is  normally  closed,  that  is, 
it  carries  a  current  when  no  messages  are  transmitted,  and 
is  therefore  called  a  closed-circuit  system.  The  connections 


® 


Fig.  2. 

of  a  closed-circuit  system  employing  relays  and  local  cir- 
cuits at  the  stations  are  shown  in  Fig.  2,  which  also  includes 
an  intermediate  station.  When  the  operator  at  station  A 


6  TELEGRAPH   ENGINEERING 

depresses  his  key  the  three  relays  R  will  be  actuated  and 
their  armatures  will  be  drawn  from  the  rear  stops  r  and 
strike  the  front  contact  screws  /,  thereby  completing  the 
three  local  circuits  and  permitting  the  local  batteries  b  to 
operate  the  sounders.  As  many  as  thirty  or  forty  inter- 
mediate stations  may  be  connected  in  series  on  a  single 
line,  but  only  one  operator  can  send  at  one  time;  all  oper- 
ators, however,  may  receive  the  message  whether  intended 
for  them  or  not.  If  another  operator  wishes  to  send  he 
must  wait  until  the  line  is  idle,  or  else,  if  the  urgency  of 
his  message  warrants,  he  may  interrupt  traffic  by  opening 
the  circuit  at  his  station  with  the  switch  s,  and  then  trans- 
mit. Such  interruption  also  takes  place  when  one  oper- 
ator wishes  to  verify  a  portion  of  a  message  transmitted  by 
another. 

The  closed-circuit  telegraph  system  is  used  throughout 
the  United  States.  It  is  important  that  the  relays  on  a 
circuit  be  of  the  same  type,  or,  more  specifically,  that  they 
have  the  same  number  of  turns  on  their  windings  for  the 
same  core  construction,  so  that  the  common  current  in  the 
circuit  will  occasion  the  same  magnetizing  force  in  each 
relay  and  insure  proper  functioning  of  the  armature. 

If  primary  or  secondary  cells  are  used  as  the  source  of 
current,  they  may  be  grouped  together  forming  one  bat- 
tery at  one  station,  may  be  divided  into  two  batteries 
located  at  the  terminal  stations,  or  may  be  apportioned 
among  the  various  stations  forming  a  number  of  separate 
batteries,  care  being  exercised  not  to  have  some  batteries 
connected  in  opposition  to  others.  A  single  battery  in  a 
circuit  conduces  to  uniform  care  of  all  cells  and  to  economy 
of  maintenance.  On  the  other  hand,  should  a  circuit  with 
a  single  battery  at  a  terminal  station  become  grounded,  all 


SIMPLEX  TELEGRAPHY 


stations  beyond  the  ground  would  be  rendered  inoperative 
and  unable  to  communicate  with  each  other.  A  ground 
on  a  circuit  with  two  terminal  batteries  prevents  through 
operation,  but  the  stations  on  each  side  of  the  ground  can 
temporarily  maintain  local  communication. 

Another  simplex  telegraph  system  is  used  extensively  in 
Europe,  namely  the  so-called  open-circuit  system,  in  which 
the  main-line  circuit  is  really  normally  closed  but  does  not 
include  a  source  of  current  when  no  messages  are  being 
transmitted.  The  system  derives  its  name  from  the  fact 
that  all  batteries  are  normally  open-circuited.  The  con- 
nections of  two  terminal  stations  and  one  intermediate 
station  using  the  open-circuit  system  are  shown  in  Fig.  3, 


Fig.  3- 

the  letters  having  the  same  significance  as  before.  The  de- 
pression of  a  key  at  a  station  introduces  the  source  of 
current  at  that  station  into  the  circuit  and  causes  the 
operation  of  the  relays  at  all  the  other  stations.  These  in 
turn  operate  the  sounders  through  the  local  batteries,  as 
before. 

In  the  open-circuit  system  the  voltage  of  the  batteries 
or  generators  at  the  various  stations  should  be  the  same 
and  sufficient  individually  to  operate  the  entire  circuit, 
whereas  in  the  closed-circuit  system  the  current  sources 
may  be  subdivided  arbitrarily  so  long  as  the  aggregate 
voltage  is  sufficient  to  operate  the  entire  circuit.  Since 


8  TELEGRAPH  ENGINEERING 

current  flows  when  no  messages  are  sent  in  the  closed- 
circuit  system,  a  greater  amount  of  electrical  energy  is 
required  for  the  operation  of  this  system  than  the  open- 
circuit  system.  When  the  connections  of  Fig.  3  are  em- 
ployed, the  sending  operator  does  not  hear  the  signals 
that  he  sends  out  on  the  line,  but  this  disadvantage  can  be 
avoided  by  shifting  the  relays  from  their  present  position 
to  the  points  on  the  line  marked  x  and  connecting  the 
back  key  contacts  directly  with  the  points  a. 

In  the  foregoing  figures  relays  and  sounders  were  rep- 
resented as  having  a  single  core,  while  in  reality  they  have 
two  cores  connected  at  the  rear  with  a  soft  iron  yoke. 
The  windings  on  the  two  cores  are  usually  connected  in 
series.  This  method  of  graphic  representation  will  be  re- 
tained for  the  sake  of  clearness. 

4.  Telegraph  Instruments.  —  Keys.  A  key  extensively 
used  on  closed-circuit  systems  is  the  Bunnell  key  illustrated 
in  Fig.  4.  It  consists  of  a  steel  lever  carrying  a  flat  hard- 


Fig.  4. 

rubber  knob  at  one  end,  and  pivoted  near  the  other  end  in 
trunnion  screws  that  are  mounted  in  uprights  extending 
from  the  elliptically-shaped  brass  base.  The  movement 
of  the  lever  is  adjustable  by  the  knurled  screw  at  its  rear 
end.  The  other  end  of  the  lever  is  kept  up  normally  by 
means  of  the  spring  shown,  the  tension  thereof  being  regu- 


SIMPLEX  TELEGRAPHY 


lated  by  the  knurled  screw  through  the  middle  of  the 
lever.  When  the  knob  is  depressed  a  platinum  point  on 
the  under  side  of  the  lever  makes  contact  with  a  similar 
point  fixed  in  a  cone-shaped  cap  fastened  to,  but  insulated 
from,  the  base.  This  latter  contact  point  is  connected 
by  a  brass  strip  to  the  front  binding  post,  which  is  also 
insulated  from  the  base;  the  other  terminal  is  fastened 
directly  to  the  base  and  therefore  is  in  metallic  connection 
with  the  contact  point  carried  on  the  lever.  An  auxiliary 
lever,  called  a  circuit-closer,  carrying  a  taller  knob,  is 
pivoted  on  the  base  to  move  horizontally,  so  as  to  engage, 
when  pressed  toward  the  key  lever,  an  extended  clip  on 
the  fixed  contact  point,  thereby  short-circuiting  the  key. 

In  holding  the  key  for  sending, 
the  index  finger  should  rest  on  the 
knob,  with  the  thumb  and  second 
finger  on  its  edge  for  steadying 
the  motion  of  the  key.  Depres- 
sing the  key  closes  or  makes  the 
circuit  and  releasing  the  key  opens 
or  breaks  the  circuit. 

Occasionally  horizontally-oper- 
ated keys  with  double  contacts 
are  employed,  requiring  but  half 
the  motions  in  the  formation  of 
telegraphic  characters  that  are 
necessary  with  the  usual  vertically- 
operated  keys.  Fig.  5  shows  the 
BunneU  "  double-speed  "  key.  The 
lever  is  attached  to  a  post  at  the  rear  end  of  the  key  by 
means  of  a  flat  spring.  It  stands  normally  midway  be- 
tween the  two  platinum  contacts  that  are  supported  in  a 


Fig.  5. 


10  TELEGRAPH  ENGINEERING 

U-shaped  piece,  mounted  on,  but  insulated  from,  the  base. 
This  connects  with  the  binding  post,  the  other  terminal 
being  the  post  which  supports  the  lever.  In  operating  the 
key,  the  knob  should  be  allowed  free  play  between  thumb 
and  finger,  and  the  hand  given  a  sidewise  rocking  motion. 
Moving  the  lever  to  the  right  or  left  closes  the  circuit. 

Many  semi-automatic  key  transmitters,  called  vibroplex 
or  mecograph  transmitters,  are  used,  and  permit  experi- 
enced operators  to  signal  faster  than  with  the  keys  already 
described.  The  horizontally-operated  lever  has  a  pendulum 
extension  having  an  adjustable  vibration  rate.  To  form  a 
dash  the  operator  holds  the  key  knob  to  the  left  for  a  suit- 
able length  of  time;  to  form  dots  the  key  is  moved  to  the 
right  and  held  there  while  the  pendulum  transmits  auto- 
matically any  desired  number  of  dots. 


Fig.  6. 

Sounders.  Fig.  6  shows  a  typical  sounder.  It  consists 
of  a  horseshoe  electromagnet  with  two  series-connected 
coils  protected  by  hard-rubber  shells,  and  a  pivoted  brass 
or  aluminum  lever  carrying  a  soft-iron  armature  properly 
placed  with  respect  to  the  magnet  poles.  The  lever  is 


SIMPLEX  TELEGRAPHY  II 

pivoted  near  one  end  in  trunnion  screws  mounted  on  an 
inverted  U-shaped  standard,  this  end  being  held  down  nor- 
mally by  a  spring  whose  compression  is  regulated  by  a 
knurled  screw  at  the  top  of  the  standard.  The  motion  of 
the  lever  is  limited  at  the  other  upright  by  the  two  screws 
at  the  left,  their  adjustment  being  fixable  by  the  locknuts. 
The  parts  mentioned  are  mounted  on  a  brass  surbase  which 
is  in  turn  mounted  on  the  wooden  base  carrying  the  bind- 
ing posts  that  connect  with  the  coil  terminals.  Perfect 
sounders  produce  a  clear  loud  tone  and  act  quickly. 

Sounders  for  main  line  use,  that  is  for  short  lines  without 
relays,  are  generally  wound  to  have  a  resistance  of  20 


Fig.  7. 

ohms,  but  many  have  resistances  up  to  150  ohms;  for 
local  circuit  use  they  are  usually  wound  to  a  'resistance  of 
4  ohms. 

For  enhancing  and  concentrating  the  signals  emitted  by 
sounders,  these  instruments  are  encased  in  resonators,  such 
as  shown  in  Fig.  7.  They  are  especially  adapted  for  oper- 


12  TELEGRAPH   ENGINEERING 

ators  located  in  large  offices  or  in  noisy  railway  stations, 
and  for  operators  using  typewriters  in  recording  received 
messages.  The  type  illustrated  is  capable  of  being  turned 
through  three-fourths  of  a  revolution,  and  is  provided  with 
a  message  clip. 

Relays.  —  A  relay  widely  used  is  shown  in  Fig.  8.  It 
consists  of  a  horizontally  mounted  electromagnet,  the  two 
cores  of  which  are  joined  at  the  back  by  a  soft-iron  yoke. 
This  electromagnet  is  movable  longitudinally  through  the 
bobbin  guide  by  means  of  the  screw  at  the  right,  so  as 
to  vary  the  length  of  the  gap  between  the  magnet  poles 


Fig.  8. 

and  the  armature,  which  is  mounted  in  front  of  them. 
This  armature  is  pivoted  at  the  lower  end,  while  the  upper 
end  or  tongue  plays  between  two  adjustable  screws,  with 
locknuts,  supported  on  the  bobbin  guide.  An  adjustable 
retractile  spring  suitably  mounted  keeps  the  armature 
normally  away  from  the  magnet  poles  and  against  the 
back  stop  screw  which  contains  a  small  piece  of  insulating 
material.  When  the  relay  is  energized  the  platinum  con- 
tact on  the  tongue  touches  a  similar  contact  in  the  front 
stop  screw  and  thereby  completes  the  local  circuit  which 
is  joined  to  the  left-hand  binding  posts.  The  right-hand 


SIMPLEX  TELEGRAPHY 


binding  posts  are  the  terminals  of  the  magnet  winding,  and 
connect  with  the  lines. 

In  practice,  relays  have  resistances  ranging  from  20  to 
300  ohms,  but  i5o-ohm  relays  are  the  most  extensively 
used.  A  i5o-ohm  relay  in  considerable  use  consists  of 
6500  turns  of  No.  30  B.  &  S.  single-silk-covered  copper 
wire  and  operates  commercially  on  0.05  ampere,  although 
it  can  be  adjusted  to  work  reliably  on  a  current  as  small  as 
o.oio  ampere.  The  average  distance  between  the  armature 
and  pole  faces  of  the  magnets  is  about  0.03  inch.  When 
traversed  by  a  25  cycle  alternating  current  of  0.08  ampere 
the  impedance  of  the  relay  is  about  550  ohms. 

The  number  of  turns  of  copper  wire  which  can  be  accom- 
modated on  any  magnet  bobbin  may  be  quickly  found  by 
multiplying  the  length  of  the  winding  space  in  inches  by  the 
permissible  depth  of  the  winding  in  inches  and  dividing  this 
result  by  a  winding  constant  for  the  selected  wire  size,  values 
of  which  constant  are  given  in  the  following  wire  table: 


B.&S. 
gage 

Diameter 
of  bare 
wire  in 
mils 

Winding  constants 

B.&S. 

gage 

Diameter 
of  bare 
wire  in 
mils 

Winding  constants 

Single-silk- 
covered 
copper  wire 

Enameled 
copper  wire 

Single-silk- 
covered 
copper  wire 

Enameled 
copper  wire 

16 

I? 
18 

19 
2O 
21 
22 
23 
24 
25 
26 

27 
28 

50.82 
45-26 
40.30 

35-89 
31.96 
28.46 
25-35 
22.57 
2O.  IO 

17.90 
15.94 

14.20 
12.64 

0.00267 
O.OO2I4 
0.00173 
0.00138 
O.OOIIO 

o  .  000884 
0.000708 
0.000568 
0.000458 
0.000370 
0.000299 
0.000244 

0.000202 

29 
30 
31 
32 
33 
34 
35 
36 
37 
38 
39 
40 

11.26 
10.03 
8.928 
7-950 
7.080 

6.305 
5-6I5 
5-ooo 

4-453 
3-965 
3-531 
3-145 

O.OOOl68 
0.000142 
O.OOOI2I 
O.OOOIO5 

o  .  0000889 

0.0000766 
0.0000658 
0.0000570 
0.0000497 
0.0000437 

o  .  0000388 

0.0000348 

0.000137 
O.OOOII3 
0.0000928 
0.0000767 
0  .  0000645 
o  .  0000484 
o  .  0000398 
0.0000334 
0.0000268 
0.0000227 

o  .  000845 
0.000673 
0.000534 
0.000413 
0.000327 
0.000267 
O.OOO2IO 
O.OOOI7O 



14  TELEGRAPH   ENGINEERING 

When  a  constant  electromotive  force  is  impressed  on  the 
terminals  of  a  relay  or  sounder  the  current  does  not  in- 
stantly assume  its  ultimate  value  because  of  the  inductance 
of  the  electromagnet.  As  the  inductance  of  a  winding 
surrounding  iron  depends  on  the  current  traversing  the 
winding  and  the  position  of  the  armature,  it  is  difficult  to 
calculate  the  growth  of  current  as  a  function  of  time  for 
these  telegraph  instruments.  The  lower  curve  of  Fig.  9 


Fig.  9. 

shows  the  growth  of  current  strength  in  a  typical  relay  as 
obtained  experimentally  by  means  of  an  oscillograph.  Ab- 
scissas represent  time  —  one  inch  corresponds  to  0.037 
second;  ordinates  represent  current  strength  —  one  inch 
corresponds  to  0.030  ampere.  The  upper  curve  shows  the 
current  in  the  circuit  controlled  by  the  relay  contacts.  It 
will  be  observed  that  one-thirtieth  of  a  second  elapses  after 
impressing  voltage  on  the  relay  coils  before  armature  chat- 


SIMPLEX  TELEGRAPHY  15 

tering  ceases  and  the  local  circuit  is  closed.  This  time, 
with  different  instruments,  varies  in  some  way  with  the 
ratio  of  the  inductance  to  the  resistance  of  the  relay. 

When  the  impressed  voltage  is  withdrawn  the  relay 
armature  is  not  immediately  drawn  back  by  the  spring  be- 
cause of  the  residual  magnetism  in  the  cores.  To  attain 
quick  release  the  armature  when  drawn  toward  the  magnet 
poles  should  not  quite  touch  them.  This  condition  is  ob- 
tained by  the  stop  screws  or  else  by  the  insertion  of  small 
non-magnetic  pins  in  the  pole  faces  so  as  to  project  about 
6*2  of  an  inch. 

Registers.  —  Where  it  is  desired  to  record  automatically 
the  received  signals,  as  in  small  telegraph  offices,  or  with 


Fig.  10. 


the  District  Telegraph  Messenger  Service,  an  ink-recording 
sounder  or  register  may  be  used.  A  register  consists  of  an 
electromagnet  and  a  pivoted  armature  lever  which  presses 
a  paper  tape  against  an  inked  wheel  when  actuated.  Spring- 


i6 


TELEGRAPH   ENGINEERING 


driven  clockwork  moves  the  tape  past  the  inked  printing 
wheel,  the  motion  beginning  at  the  first  current  impulse 

and  ending  some  seconds 
after  the  last  impulse.  Fig. 
10  shows  a  register  and 
Fig.  ii  shows  an  automatic 
paper  winder  used  with  it 
for  winding  up  the  paper  as 
it  is  delivered  from  the  reg- 
ister. 

5.  Best  Winding  for  Re- 
ceiving Instruments.  —  On  a 
telegraph  line  the  windings 
on  the  receiving  instruments 
might  have  many  turns  of 

small  wire  or  fewer  turns  of  larger  wire  for  the  same  wind- 
ing space.  The  former  windings  require  a  smaller  current 
than  the  latter  for  a  given  magnetizing  force,  but  at  the 
same  time  have  a  greater  resistance.  On  reflection  it  will 
be  observed  that  a  best,  winding  exists  for  each  set  of 
conditions,  which  winding  results  in  the  greatest  transmis- 
sion distance  for  lines  of  given  cross-section.  The  method 
of  determining  this  ideal  winding  is  given  below. 

If  A  be  the  winding  space  on  an  electromagnet  in  square 
inches  and  d  be  the  diameter  of  the  wire  over  insulation  in 
inches,  the  number  of  turns  will  be 

A 

n  =  -,  (2) 

which  takes  no  account  of  bedding  of  wires  in  preceding 
layers  or  of  interleaving  insulation.  If  D  be  the  wire 
diameter  in  mils,  and  z  be  the  mean  length  of  a  turn  in 


SIMPLEX   TELEGRAPHY  17 

inches,  the  resistance  of  the  copper  wire  forming  the  wind- 
ing will  be 

0.87  nz    .  ,  v 

Rr  =    —jy-  ohms  (3) 

at  20°  cent.,  where  the  constant  0.87  is  the  resistance  of  a 
copper  wire  i  inch  long  and  o.ooi  inch  in  diameter. 

The  steady  current  traversing  the  circuit  of  length  / 
miles  with  N  identical  relays  in  series  for  an  impressed 
unidirectional  voltage  E  is 


where  R  is  the  line  resistance  per  mile.  The  line  is  assumed 
perfectly  insulated  from  ground.  Therefore  the  ampere- 
turns  are 

EA 

nl  = 

from  which 

l=Rd2(nJ~ 
Taking  g  as  the  thickness  of  insulation  in  inches, 

d  =  -    -  +  2  g  inches, 


In  order  to  find  the  maximum  distance  of  transmission  as  a 
function  of  wire  diameter,  this  equation  is  differentiated 
with  respect  to  D  and  equated  to  zero.  Whence 

^3  _  i.742JV(tt/)  D_  irfiozgN  (nl)  = 
E  E 


i8 


TELEGRAPH  ENGINEERING 


which  is  of  the  form  Z)3  -  PD  -  Q  =  o.     The  solution  of 
this  form  is 


—  cos 


-cos 


-1 


\* 


mils. 


(6) 


This  result  gives  the  size  of  wire  to  be  used  in  winding  the 
coils  of  the  receiving  instrument,  and  substituting  this 
value  in  equation  (3)  gives  the  instrument  resistance. 

As  a  numerical  illustration  consider  relays  having  the 
following  constants: 

Sectional  area  of  winding  on  both  coils  =  A  =  i.o  sq.  in., 

Mean  length  of  turn  =  z  =  2.4  inches, 

Number  of  relays  in  circuit  =  N  =  10, 

Impressed  voltage  =  £  =  120  volts, 

Ampere-turns  necessary  for  actuation  =  nl  =  200, 

Thickness  of  silk  insulation  =  g  =  o.ooi  inch. 
For  these  values 


I.74ZJV  (nl) 
E 


1.74  X  2.4  X  10  X  200      ,    , 
-  =  69.6, 


1 20 


Q  =  1000  gP  =  1000  X  o.ooi  X  69.6  =  69.6, 
and  consequently  the  wire  diameter  for  the  relay  is 

69.6 


D 


cos 


-cos 


-1 


_ 

=  2  V23.2cos(|  cos"1 0.312)  =9.632  cos  23°57'  =  8. 80 mils. 

*  If  the  bracketed  expression  is  greater  than  unity,  hyperbolic  cosines 
are  taken.     For  cosine  tables  see  the  Appendix. 


SIMPLEX  TELEGRAPHY  19 

The  nearest  standard  wire  size  hereto  is  No.  31  B.  &  S. 
gage,  for  which  D  =  8.93  mils.  Using  No.  31  wire,  the 
number  of  turns  on  both  relay  bobbins  is 

_  i  .00  _  _  o  A 

(0.00893  +  0-002)2  - 

and  the  resistance  of  the  instrument  is 
0.87  nz      0.87  X  8360  X  2.4 

--     =  2I9  ohms- 


Thus  the  ideal  relay  winding  for  the  given  conditions 
would  consist  of  8360  turns  of  No.  31  copper  wire  having 
a  resistance  of  219  ohms.  With  10  of  these  instruments 
the  maximum  distance  of  telegraphic  transmission  is  such 
that  the  resistance  of  the  whole  line  exclusive  of  relays  is 
(from  equation  4) 

En       A7r>       120  X  8360 

--  NRr  =  -        —  *  --  10  X  219  =  2826  ohms. 
200  200 

Using  a  i2.4-ohm-per-mile  line,  this  means  a  transmission 

distance  of  --  =  228  miles. 
12.4 

•  The  dependance  of  the  ideal  winding  upon  the  impressed 
voltage  and  number  of  relays  used  in  the  circuit,  for 
otherwise  identical  conditions  assumed  in  the  foregoing 
illustration,  is  shown  in  the  table  on  the  following  page. 

The  same  method  may  be  used  in  determining  the  most 
suitable  windings  for  main-line  sounders. 

In  practice  there  are  various  standard  relay  and  sounder 
'resistances,  and  for  a  given  set  of  conditions,  that  type  of 
instrument  winding  is  selected  which  will  approach  closely 
to  the  ideal  winding.  Usual  resistances  of  receiving  instru- 
ments are  20,  50,  75,  100,  150,  250  and  300  ohms.  Main- 


2O 


TELEGRAPH   ENGINEERING 


line  relays  of  37.5  ohms  resistance  are  also  used  on  many 
commercial  and  railway  telegraph  lines. 


40  Volts 

80  Volts 

Number 
of 
relays 

Calcu- 
lated 
wire  di- 
ameter, 
in  mils 

Nearest 
B.  &S. 
gage 
num- 
ber 

Relay 
resist- 
ance in 
ohms 

Maximum 
line  resist- 
ance exclu- 
sive of 
relays 

Calcu- 
lated 
wire  di- 
ameter 
in  mils 

Nearest 
B.  &S. 
gage 
num- 
ber 

Relay 
resist- 
ance in 
ohms 

Maximum 
line  resist- 
ance exclu- 
sive of 
relays 

2 

6.QI 

33 

506 

1416 

S-oi 

36 

1700 

4760 

6 

11.67 

29 

94 

576 

8-37 

32 

334 

2036 

IO 

14.94 

27 

39-5 

367 

10.70 

29 

94 

1340 

is 

18.2 

25 

16.4 

258 

12.90 

28 

61 

949 

20 

2^.9 

24 

10.6 

198 

14.94 

27 

39-5 

734 

30 

25-5 

22 

4-36 

137 

18.20 

25 

16.4 

5i6 

120  VoltS 

160  Volts 

6 

6.91 

33 

5o6  ' 

4248 

6.04 

34 

762 

7028 

IO 

8.80 

3i 

219 

2826 

7.68 

32 

334 

4740 

13 

9-99 

30 

144 

2274 

8.70 

3i 

219 

384i 

16 

11.02 

29 

94 

1916 

9.60 

30 

144 

3224 

20 

12.28 

28 

61 

1576 

10.70 

29 

94 

2680 

30 

14-94 

27 

39-5 

IIOI 

12.90 

28 

61 

1898 

6.  Sources  of  Current.  —  In  telegraphy  the  current  for 
main  and  local  circuits  is  furnished  occasionally  by  primary 
batteries  (such  as  Gravity,  Fuller,  Edison-Lalande,  Dry, 
and  Leclanche  cells),  more  frequently  by  storage  or  second- 
ary batteries,  but  is  furnished  chiefly  by  dynamo  electric 
machines. 

Primary  Batteries.  —  Primary  cells  consist  of  two  dissim- 
ilar metals  (or  one  may  be  carbon)  immersed  in  an  electro- 
lyte; and  when  these  are  connected  externally  by  means  of 
an  electric  circuit,  the  chemical  energy  of  the  cell  is  gradually 
converted  into  electrical  energy,  and  a  current  is  main- 
tained in  the  circuit.  By  this  action  one  of  the  metal 
electrodes,  the  anode,  is  slowly  consumed.  To  prevent 


SIMPLEX  TELEGRAPHY  21 

the  adhesion  of  liberated  gas  at  the  other  electrode,  or 
cathode,  during  current  delivery,  a  depolarizer  is  em- 
ployed which  combines  readily  with  the  gas  evolved.  In 
some  cells,  as  in  the  Fuller  and  Leclanche  types,  the  cathode 
and  depolarizer  are  contained  in  porous  cups.  When  com- 
mercial metals  containing  impurities  are  used,  the  anode  is 
also  consumed  by  local  action  without  contributing  to  the 
production  of  current  in  the  circuit.  This  deleterious  proc- 
ess, which  goes  on  whether  the  cell  delivers  current  or  not, 
is  minimized  by  amalgamation  of  the  anode. 

Cells  such  as  the  Gravity,  Fuller  and  Edison-Lalande 
types  are  suitable  for  closed-circuit  work,  while  the  Dry 
and  Leclanche  cells  are  suitable  for  intermittent  service. 

Of  primary  batteries  the  Gravity  cell  is  the  most  exten- 
sively used  in  telegraphy.  Fig.  12  shows  the  Crow-foot 
gravity  cell,  the  copper  being  placed  in 
the  bottom  of  the  jar  and  the  zinc  sus- 
pended from  the  upper  edge.  Zinc 
sulphate  (ZnS04)  is  the  electrolyte  and 
copper  sulphate  (CuS04)  is  the  depo- 
larizer of  this  cell,  which  yields  a  volt- 
age of  about  i.o,  and  has  an  internal 
resistance  of  approximately  2  to  3  ohms. 

When  a  battery  furnishes  current  to 
several  circuits,  its  internal  resistance 
causes  the  current  in  each  circuit  to  become  less  as  the 
number  of  circuits  connected  in  parallel  to  the  same  bat- 
tery increases. 

Storage  Batteries.  —  Storage  or  secondary  batteries  are 
reversible  cells  which  can  be  charged  from  some  source  of 
direct  current  and  later  discharged.  Charging  increases 
the  chemical  energy  of  the  cell,  and  this  energy  reverts  to 


22 


TELEGRAPH  ENGINEERING 


electrical  energy  during  discharge.  The  usual  form  of 
storage  battery  consists  of  a  lead  peroxide  (PbC^)  positive 
grid  and  a  spongy  lead  (Pb)  negative  grid  in  an  electrolyte 
.of  dilute  sulphuric  acid  of  specific  gravity  1.2.  During 
discharge  these  electrodes  are  gradually  changed  to  lead 
sulphate  (PbSC^),  a  poor  conductor  of  electricity.  Re- 
charge converts  the  electrodes  to  their  initial  states.  The 
voltage  of  the  cells  when  fully  charged  is  2.5,  and  the  voltage 
beyond  which  it  is  inadvisable  to  discharge  them,  because 
of  otherwise  excessive  sulphating,  is  1.8. 

The  rating  of  these  storage  bat- 
teries in  ampere-hours  is  based  on 
a  uniform  8-hour  discharge.  A  more 
rapid  discharge  results  in  a  lowered 
ampere-hour  capacity.  The  capacity 
of  a  cell  depends  primarily  on  the 
size  and  number  of  plates  and  their 
character,  and  is  generally  from  40 
to  60  ampere-hours  for  each  square 
foot  exposed  surface  of  positive  plate. 
Fig.  13  shows  a  56o-ampere-hour 
storage  cell  made  by  the  Electric 
Storage  Battery  Company. 
Fig* I3*  The  Edison  storage  battery  is  also 

suitable  for  telegraphic  purposes.  Its  positive  electrodes 
consist  of  grids  of  nickel-plated  steel  supporting  nickel 
oxide  intermixed  with  flakes  of  pure  nickel,  and  the  nega- 
tive electrodes  consist  of  similar  grids  containing  iron 
oxide.  The  electrolyte  is  a  21  per  cent  solution  of  caustic 
potash  in  distilled  water  and  is  contained  in  a  nickel-plated 
sheet-steel  case. 
The  ampere-hour  capacity  of  these  batteries  is  based  on 


SIMPLEX   TELEGRAPHY 


a  5-hour  discharge  rate.  The  voltage  of  a  cell  is  1.2  at 
normal  discharge;  for  charging  1.85  volts  are  required  per 
cell.  Fig.  14  shows  the  appearance  of  an  8o-ampere-hour 


Fig.  14. 

Edison  storage  battery,  and  also  the  positive  (at  the  right) 
and  negative  plates. 

Storage  cells  may  be  charged  directly  from  direct-current 
service  mains  or  through  boosters  and  motor-generators. 
If  only  alternating  current  is  available,  it  may  be  changed 
into  direct  current  for  the  charging  of  storage  batteries  by 
means  of  electrolytic  or  mercury-vapor  rectifiers,  or  by 
means  of  converters  or  motor-generators. 

Generators.  —  Electric  generators  are  extensively  used  in 
large  telegraph  offices  for  the  operation  of  long  lines  and 
local  instruments.  They  may  be  driven  by  steam  or  gas 
engines,  but  more  generally  by  electric  motors  which  re- 
ceive either  direct  or  alternating  current  from  service 
mains.  For  the  operation  of  telegraph  circuits  of  all  types 
different  voltages  are  required  from  about  25  to  400  volts. 

The  voltages   now  considered   standard   for   main-line 


TELEGRAPH   ENGINEERING 


operation  are  80,  160,  240  and  320  by  the  Western  Union 
Telegraph  Company,  and  85,  125,  200  and  385  by  the 
Postal  Telegraph-Cable  Company,  while  for  local  circuit 
operation  they  are  26  and  52  with  the  former  and  40  volts 


Fig.  15- 

with  the  latter  company.  The  generators  for  the  two  higher 
voltages  are  generally  duplicated  so  as  to  permit  of  re- 
versal of  potential,  as  necessary  in  duplex  and  quadruplex 
service  (see  Chapters  II  and  III).  With  printing  tele- 
graph systems  no  volts  are  generally  used. 


Fig.  16. 


The  arrangement  of  generators  at  a  telegraph  office  is 
shown  in  Fig.  15,  the  voltages  indicated  being  those  of  the 
Postal  Telegraph-Cable  Company.  Protective  resistances, 
r,  in  series  with  the  generators,  are  used  to  prevent  injury 
to  the  machines  in  case  of  line  short-circuits,  etc.  Fig.  16 


SIMPLEX  TELEGRAPHY  25 

shows  the  appearance  of  General  Electric  Company  motor- 
generator  sets  each  composed  of  a  direct-current  motor 
and  generator.  The  22O-volt  3 -wire  direct-current  system 
with  neutral  wire  grounded  is  sometimes  used,  where  avail- 
able, for  telegraphic  purposes.  Dynamotors  and  mercury- 
vapor  rectifiers  are  also  frequently  employed. 

It  is  common  practice  to  have  a  source  of  electromotive 
force  at  both  ends  of  simplex  lines  instead  of  a  single 
source  of  equal  total  voltage  at  one  end,  because  of  better 
line  operating  characteristics  during  wet  weather. 

7.  Telegraph  Codes.  —  Telegraph  codes  consist  of  vari- 
ous combinations  of  dots,  dashes  and  spaces  for  the  rep- 
resentation of  letters,  numerals  and  punctuation  marks. 
Two  codes  are  in  extensive  use,  the  American  Morse,  or 
simply  Morse,  and  the  Continental  Morse,  or  simply  Con- 
tinental. The  Morse  code  is  used  throughout  the  United 
States  and  Canada  for  overland  signalling  except  in  print- 
ing telegraphy.  In  punctuation,  however,  the  Phillips 
Punctuation  code  has  generally  superseded  it  because  of 
its  greater  completeness.  The  Continental,  or  so-called 
universal  code,  is  in  use  throughout  the  world  for  sub- 
marine telegraphy  and  also  in  almost  every  country  except 
those  mentioned  for  overland  signalling.  The  codes  are 
given  on  the  two  pages  following. 

In  the  code  characters  the  length  of  a  dot  is  taken  as 
the  unit  of  measurement  of  dashes  and  spaces.  The  ordi- 
nary dashes  are  three  times  as  long  as  dots,  the  long 
dashes  for  letter  /  and  cipher  in  the  Morse  code  are  re- 
spectively five  and  seven  times  as  long  as  a  dot,  the  spaces 
between  the  elements  of  letters  are  equal  to  dots,  the 
longer  spaces  in  the  letters  C,  0,  R,  Y,  Z  and  &  of  the 


26 


TELEGRAPH   ENGINEERING 


ALPHABET 


LETTERS 
A 
B 
C 
D 
E 
F 
G 
H 
I 

J 
K 
L 

M 
N 
O 
P 

Q 

R 
S 
T 
U 
V 
W 

•  x 

Y 
Z 

& 

FIGURES 
1 

2 
3 
4 
5 
6 
7 
8 
9 
0 


MORSE 


CONTINENTAL 


MORSE 


NUMERALS 

CONTINENTAL 

-  — or 

or 


or    - 


-  -    or    — 

or  • 

or 


SIMPLEX  TELEGRAPHY 


fore  words 
tter 
,  repeat 

i.     1: 

r  i 
ll  h 

2,    2? 

II 

i 

i 

i 

i 

jS*' 

1 

PHILLIPS 

i 

•  1 

i    i 
II 

j 

i    i 

j  1 

i    f    i 

;  ;  i  : 
!!;i 

i 
;i 

1  1 

i      1 

j! 

i 

1 

i 

1  1 

1'  1 

I1  ' 
ll  1 

II  1 

„       ' 

ii  !: 

ii     M 

1 

1 
i    i 

::i: 

•  1  1 

:•  ! 

!  i 

| 

II  1 
II  1 

ii  n 

i 

1  1 

i 

i  i 

I  i  i  i 
i  1  i  i  i 

•  i  i 
i  i  i 

1  !    1 

1  1 

! 

111 

ii     1  1 
il    ii 

0 

i 

i 

i 
i 

1 

/ 

1VJLN3N 

i  i 

1      1 

i 
I 

i 

:  i 

i   i 

jj 

i 

I 

SCTTJATIO 

1; 

i  ! 
i  i 

1 
i 

1 

i 

1   i 

1  1 
:  i 

I    :' 
1    i! 

i 
i 

I 
j 

i 
i 

1 

i 

i 

£ 

i 

i 

i 

i   i 

I 

1 

1   i 

1 

ll 

I 

O    1 

1      i 

i 

i  I 

i 

1 

1 

i  ! 

1 

i 

i  1 

1  1 

1 

i 
,  I 

1 

s-^>~~- 

^£ 

c 

co    a 

T3 

.2 

& 

*J 

0    C    <-> 

-2  -2'i 

Comma 

Interrogation 
Exclamation 

ijfj 

fa  QE  <Q 

#* 

~C    d 

£  S 

CO 

«    bO 

™   c   S 
C    3  =5 

v  o  *2 

Pence 
Capitalized  lette 
Colon  followed 
quotation 

Decimal  point 
Paragraph 

1 

5 

0 

M 

0 

1 

Parenthesis 
Brackets 

Quotation  mark 
Quotation  withi 

quotation 
»..»»<• 

28  TELEGRAPH   ENGINEERING 

Morse  code  are  twice  as  long  as  dots,  and  the  spaces  be- 
tween letters  and  between  words  are  respectively  three  and 
six  times  as  long  as  dots. 

The  Continental  code,  having  more  dashes  than  the 
Morse  code,  requires  a  little  longer  time  in  the  transmission 
of  any  given  message  expressed  in  that  code  than  when 
expressed  in  Morse  code. 

A  partial  list  of  abbreviations  used  in  commercial  teleg- 
raphy follows: 

Scotus  —  Supreme  Court  of  the  United  States 

Bk— Break 

Ck  — Check 

Fm  —  From 

Ga  —  Go  ahead 

Min  —  Wait  a  minute 

Nm  —  No  more 

No  —  Number 

x  (placed  after  check)  —  Get  reply  to  message 

x  x  x  ...  —  Omission 

4  —  Where  shall  I  go  ahead? 

8  —  Wait,  I  am  busy 

Thus,  in  case  of  doubt  as  to  the  accuracy  of  a  transmitted 
message,  the  receiving  operator  breaks  and  sends  the  let- 
ters bk,  ga  and  the  last  word  correctly  received;  whereupon 
the  sending  operator  continues  from  that  word.  Abbre- 
viations used  in  differentiating  the  various  classes  of  tele- 
graphic service  are  given  in  §  8  of  Chap.  V,  and  of  cable 
service  are  given  in  §  10  of  Chap.  XI. 

'•x 
8.  Telegraph    Lines.  —  Galvanized    iron,    hard-drawn 

copper  and  occasionally  steel  wire  are  used  for  telegraph 
lines.  The  sizes  generally  employed  on  overhead  lines  are 


SIMPLEX  TELEGRAPHY 


29 


from  No.  9  to  14  B.  &  S.  (Brown  &  Sharpe)  gage  copper 
wire  and  from  No.  4  to  12  B.  W.  G.  (Birmingham  Wire 
Gage)  iron  wire.  The  increasing  use  of  hard-drawn  copper 
wire  for  telegraph  lines  is  due  to  its  having  a  lower  resist- 
ance than  iron  for  the  same  tensile  strength,  and  to  the 
fact  that  it  is  practically  non-corrosive.  Telegraph  con- 
ductors in  cables  for  transmission  over  relatively  short 
distances  are  of  from  No.  14  to  19  B.  &  S.  soft  copper. 

The  weights,  diameters  and  resistances  of  telegraph  line 
wires  are  given  in  the  following  table: 


Hard-drawn  copper  wire 

Galvanized  iron  wire  (E.  B.  B.  quality) 

B.&S. 
Gage 
No. 

Diameter 
in  mils 

Weight  in 
pounds  per 
mile 

Resistance 
at  60°  fahr. 
per  mile  in 
ohms 

B.W.G. 
No. 

Diam- 
eter in 
mils 

Weight  in 
pounds  per 
mile. 

Resistance 
at  60°  fahr. 
per  mile  in 
ohms. 

9 
10 
II 
12 
13 
14 

114.4 
IOI.Q 
90.74 
80.  81 
71.96 
64.08 

208 

166 
132 
105 
83 
65 

4.22 
5-28 
6.6s 
8.36 

10.55 
13.29 

4 
6 

8 

9 
10 
ii 

12 

238 
2  2O 
203 

180 

165 

148 

134 
1  20 
109 

787 
673 
573 
450 
378 
305 
250 

200 
165 

5-97 
6.98 

8.20 

10.44 
12.43 
I5-4I 
18.80 
23-50 
28.48 

Soft  copper  wire 

14 

11 

17 
18 

19 

64.08 
57-07 
50.82 
45-26 
40.30 
35  89 

65 
52 
42 
32 
25.6 
20.7 

13.12 
16.54 
20.67 

26.55 
33-6o 
41.47 

Temperature  rise  increases  the  resistance  of  copper 
0.24  per  cent  per  degree  fahr.  and  increases  that  of  iron 
0.35  per  cent  per  degree  fahr.  reckoned  from  o°  fahr. 

Copper-clad  or  bimetallic  wire  is  also  used  to  some  extent 
for  telegraph  lines.  It  consists  of  a  steel  core  to  which  is 
welded  a  coating  of  copper,  forming  a  wire  of  high  tensile 


30  TELEGRAPH   ENGINEERING 

strength  and  fairly  low  resistance.  Several  grades  are 
available  that  differ  in  conductivity,  depending  upon  the 
relative  amounts  of  copper  and  steel  used. 

Bare  overhead  conductors  are  supported  by  glass  insu- 
lators mounted  on  wooden,  or  sometimes  concrete  and  steel 
telegraph  poles.  These  points  of  support  offer  leakage  cur- 
rent paths  from  the  conductor  to  ground.  Even  in  dry 
weather  the  insulation  resistance  between  the  conductor 
and  ground  is  not  infinite,  but  of  the  order  of  10  to  100 
megohms  per  mile  of  line,  while  in  wet  and  foggy  weather 
the  insulation  resistance  may  fall  to  a  fraction  of  i  megohm 
per  mile. 

In  the  foregoing  pages  only  perfectly  insulated  lines  were 
considered.  On  actual  lines,  because  of  the  distributed 
nature  of  the  leakage  paths,  it  is  more  difficult  to  determine 
the  exact  relation  between  the  various  factors  involved. 
A  rough-  approximation  on  lines  of  short  or  medium  length 
to  the  actual  conditions  is  obtained  by  considering  all  the 
leakage  paths  to  be  grouped  into  one  equivalent  path  at 
the  middle  point  of  the  line,  as  shown  in  Fig.  17. 


Fig.  17. 

It  is  evident  from  the  figure  that  even  though  the  circuit 
is  open  at  one  station,  current  flows  from  the  battery  at  the 
other  station  through  the  relay,  part  of  the  line,  and  the 
equivalent  leakage  path  to  ground.  It  follows,  therefore, 
that  at  no  time  is  the  current  flow  in  the  receiving  in- 


SIMPLEX  TELEGRAPHY  31 

struments  wholly  interrupted;  and  consequently  their  re- 
tractile springs  must  be  adjusted  to  release  the  armatures 
on  a  certain  minimum  current  strength.  In  damp  weather 
when  the  insulation  resistance  of  the  line  is  lowered  the 
relays  must  be  more  delicately  adjusted,  because  the 
currents  flowing  in  the  circuit  when  one  switch  and  when 
both  switches  are  closed  are  more  nearly  equal. 

Thus,  on  a  6oo-mile  No.  9  B.  &  S.  aerial  copper  line 
having  a  25o-ohm  relay  and  an  80- volt  battery  at  each 
end,  and  having  an  insulation  resistance  of  10  megohms 
per  mile,  the  steady  current  traversing  the  relay  when  one 
key  is  open  is 

/  = =  0.0044  ampere, 

.     10,000,000 
250  +  300  X  4-22  +  - 

ooo 
and  when  both  keys  are  closed  the  current  is 

7  =  —  -  =  0.0528  ampere. 

2  X  250  +  600  X  4.22 

On  the  other  hand,  if  the  insulation  resistance  be  taken  as 
one-half  megohm  per  mile,  the  current  when  one  key  is 
open  would  be 

80 
7  = =0.034  ampere, 

250  +  300  X  4-22  +  S00?000 
ooo 

showing  that  under  these  conditions  the  relay  must  be 
adjusted  to  operate  on  0.0528  ampere  and  release  the 
armature  on  0.034  ampere.  If  so  adjusted  and  if  the  in- 
sulation resistance  falls  still  lower,  the  line  would  be  ren- 
dered inoperative. 
With  assigned  insulation  resistance,  terminal  resistance 


32  TELEGRAPH  ENGINEERING 

and  relay  adjustment,  it  is  possible,  on  the  basis  of  the 
foregoing  paragraphs,  to  determine  the  maximum  permis- 
sible length  of  line  for  line  conductors  of  any  size.  Let 

/  =  maximum  length  of  ground-return  line  in  miles, 
R  =  line  resistance  per  mile  in  ohms, 
Rr  =  resistance  of  each  relay  in  ohms, 
N  —  number  of    relays  in  circuit  (assumed  uniformly 

distributed  between  terminal  stations), 
R{  =  insulation  resistance  per  mile  in  ohms, 
E  =  voltage  impressed  at  each  end  of  line, 
/!  =  current  in  amperes  necessary  to  actuate  relay,  and 
72  =  current  in  amperes  which  will  just  cause  release 
of  armature, 


r  4.    -* 

I  "  [       7 

2      2     / 


and 


Eliminating  E  from  equations  (7)  and  (8),  and  solving  for  I, 
there  results, 


n,r  2.. 

IT'  -R(h-ij- 

from  which  the  maximum  transmission  distance  is 


an  expression  not  involving  the  impressed  voltage. 

As  a  numerical  illustration,  consider  a  No.  9  B.  &  S. 
copper  conductor  having  a  25o-ohm  relay  at  each  end 
which  is  adjusted  to  operate  on  0.06  ampere  and  .release 


SIMPLEX  TELEGRAPHY  33 

on  0.04  ampere.     For  an  insulation  resistance  of  |  megohm 
per  mile,  the  maximum  permissible  length  of  line  is 


//  250  \2.   2  X  0.04  X  500,000 

V  V  4.22  /  4.22  (0.06-0.04) 


2  X  4-22 

=  -  59-3  +  691.0  =  631.7  miles. 
The  voltage  of  the  battery  at  each  end  should  be 

E  =  ^  (NRr  +  Rl)  =  —  (2  X  250  +  4-22  X  631.7) 

2  2 

=  95  volts, 

as  obtained  by  using  equation  (8). 

This  approximate  solution  of  the  telegraph  circuit  will 
be  referred  to  again  because  it  is  less  involved  than  the 
exact  solution  which  is  considered  in  Chap.  X.  Experi- 
ence has  proven  that  the  maximum  distance  of  trans- 
mission on  long  aerial  lines  is  limited  principally  by  line 
leakage. 

9.  Speed  of  Signalling.  —  The  speed  with  which  signals 
may  be  transmitted  over  a  telegraph  line  depends  upon 
three  factors,  namely  the  speed  of  the  sending  operator, 
the  nature  of  the  line,  and  the  responsiveness  of  the  receiv- 
ing instrument. 

An  experienced  operator  can  send  from  30  to  40  five- 
letter  words  per  minute  by  hand  transmission.  Semi- 
automatic devices  may  be  availed  of  to  raise  this  sending 
speed.  Much  higher  speeds  are  attainable  by  automatic 
transmitters,  as  described  later  (§  i,  Chap.  IV). 

It  was  pointed  out  in  the  last  section  that  the  current 
through  the  receiving  device  connected  to  a  leaky  line 
does  not  cease  altogether  upon  opening  one  key.  It  is 


34  TELEGRAPH  ENGINEERING 

evident  that  the  greater  the  line  insulation  resistance  the 
more  rapid  will  be  the  current  change  in  the  relay  coils 
with  movements  of  the  key,  and  consequently  the  quicker 
the  actuation  and  release  of  the  relay  armature.  On  a 
long  line  with  considerable  leakage,  rapid  signalling  may 
cause  the  duration  of  contact  for  dots  to  be  so  short  as  to 
prevent  the  current  in  the  relay  from  attaining  a  value 
sufficient  to  attract  its  armature.  More  deliberate  or 
"heavy  "  sending  must  then  be  resorted  to,  implying 
slower  signalling  speed.  Thus,  the  shorter  the  line  the 
higher  may  be  the  speed  of  signalling. 

Further,  the  line  itself,  especially  if  a  cable,  limits  the 
speed  of  transmission.  As  most  large  telegraph  offices  are 
in  the  business  centers  of  cities,  short  sections  of  nearly  all 
long  aerial  lines  are  placed  in  cables  under  ground  and  there- 
fore the  speed  of  signalling  on  these  lines  is  limited  by  the 
cable  sections.  In  cables  a  conductor  is  very  near  its 
return  conductor  or  the  grounded  sheath,  and  conse- 
quently its  electrostatic  capacity  is  high.  It  will  be 
shown  in  §  4  of  Chap.  XI,  that  the  signalling  speed  over 
cables  (having  negligible  inductance  and  leakance)  is  in- 
versely proportional  to  the  product  of  total  line  capacity 
and  total  line  resistance.  That  is,  if  C  be  the  capacity  in 
farads  per  mile  of  conductor,  and  R  be  the  resistance  in 
ohms  per  mile,  then 

V       Signalling  speed  »     JL_  ^L.,  (IO) 


where  /  is  the  length  of  the  cable  in  miles.     This  propor- 
tionality shows  that  for  a  given  size  of  cable  the  signalling 
speed  varies  inversely  with  the  square  of  its  length. 
It  is  safe  to  say  that  the  speed  possibilities  on  long 


SIMPLEX  TELEGRAPHY  35 

fairly  well  insulated  aerial  lines  even  with  short  cable  sec- 
tions is  greater  than  the  operating  speed  of  the  receiving 
instruments.  In  §  4  it  was  stated  that  the  time  of  current 
growth  in  a  relay  depends  upon  the  ratio  of  its  inductance 
to  its  resistance.  Rather  than  increase  the  relay  resistance 
to  obtain  rapid  response,  it  is  more  advisable  to  reduce  its 
inductance.  This  may  be  done  by  decreasing  the  number 
of  turns,  by  connecting  the  two  coils  in  parallel  instead 
of  in  series,  by  increasing  the  reluctance  of  the  magnetic 
circuit  either  by  removing  the  iron  yoke  or  by  lengthening 
the  air  gap  between  armature  and  magnet  cores,  and  by 
using  a  shunting  condenser.  Some  of  these  suggestions, 
however,  conflict  with  the  conditions  for  maximum  mag- 
netization with  a  given  current. 

The  necessary  mass  of  the  relay  armature  should  be 
apportioned  in  such  a  way  as  to  possess  the  least  moment 
of  inertia  about  the  pivots  so  as  to  acquire  a  high  velocity 
under  the  action  of  a  given  force.  The  greater  part  of 
its  mass  should  therefore  be  near  the  axis.  The  contact 
points,  however,  are  preferably  placed  far  from  the  pivots 
in  order  to  reduce  the  angular  motion  of  the  armature  and 
permit  signals  to  follow  each  other  in  rapid  succession. 
By  embodying  the  features  mentioned  relays  have  been 
constructed  which  respond  to  signals  sent  at  speeds  as 
high  as  400  words  per  minute. 

10.  Simplex  Repeaters.  —  It  was  shown  in  §  8  that 
leakage  is  the  important  factor  in  limiting  the  distance  of 
telegraphic  signalling.  Using  a  No.  9  B.  &  S.  copper  con- 
ductor with  two  25o-ohm  relays  with  given  adjustment 
(which  implies  a  given  signalling  speed)  it  was  found  that 
the  maximum  permissible  length  of  line  is  631.7  miles 


36  TELEGRAPH  ENGINEERING 

when  the  insulation  resistance  is  assumed  as  J  megohm 
per  mile.  If  a  No.  6  wire,  which  has  double  the  cross- 
section  (R  =  2.09),  were  used  instead,  the  maximum  length 
of  line  under  otherwise  identical  conditions  would  be  865.9 
miles.  Thus,  using  a  conductor  of  twice  the  size  and 
costing  twice  as  much  would  only  increase  the  distance  of 
transmission  37  per  cent.  It  is  apparent  from  this  illus- 
tration that  the  cost  of  transcontinental  telegraphy  over  a 
single  continuous  circuit  would  be  prohibitive. 

If  such  long  lines  are  subdivided  into  several  shorter 
sections,  say  from  300  to  600  miles  in  length,  each  section 
terminating  in  a  relay,  signals  may  be  automatically  trans- 


Fig.  18. 

mitted  thereby  into  the  next  section,  and  so  on  to  the 
terminus  of  the  line,  without  requiring  unduly  large  lino 
conductors.  The  speed  of  signalling  will  then  be  that  of 
the  section  which  allows  the  slowest  transmission  less  the 
speed  loss  in  the  relays.  Two-line  sections  of  such  an 
arrangement  are  shown  in  Fig.  18,  from  which  is  seen  the 
possibility  of  transmitting  toward  the  right,  but  also  the 
futility  of  endeavoring  to  transmit  in  the  opposite  direc- 
tion. In  order  to  permit  of  signalling  in  either  direction, 
the  intermediate  relays  R^  R3  .  .  .  are  replaced  by  re- 
peater sets. 
A  repeater  set  consists  of  two  relays  and  two  transmit- 


SIMPLEX  TELEGRAPHY 


37 


ters  which  are  electrically  and  mechanically  arranged  to 
allow  signalling  in  either  direction  and  in  such  a  way  as 
to  automatically  prevent  one  transmitter  breaking  at  the 
repeater  station  the  line  circuit  which  it  controls  when 
that  circuit  is  repeating  into  the  other.  Two  standard 
closed-circuit  repeaters  which  accomplish  these  results  will 
now  be  described. 

Weiny-Phillips  Repeater.  —  The  connections  of  a  Weiny- 
Phillips  repeater  set  are  shown  in  Fig.  19,  in  which  T  and  Tf 


are  the  transmitters,  and  R  and  R'  are  the  relays.  Each 
relay  has  an  extra  magnet,  H  or  H' ',  called  a  holding-coil, 
mounted  above  the  ordinary  magnets  so  as  to  act  on  the 
same  moving  element,  as  illustrated  in  Fig.  20.  Its  wind- 
ing has  a  tap  at  its  middle  point,  so  that  if  current  enters 
at  this  point,  it  will  traverse  the  two  parts  of  the  winding, 
a  and  b,  in  opposite  directions,  and  consequently  produce 
no  magnetization  in  the  core.  The  transmitter  T  has  a 
small  auxiliary  lever  m,  insulated  from  and  controlled  by 
the  main  lever,  each  lever  making  contact  with  a  platinum 


TELEGRAPH   ENGINEERING 


contact  point  when  the  magnets  of  the  transmitter  are 
energized.     The    switches  5   and   s'   on    the    transmitters 


Fig.  20. 


enable  an  operator  to  sever  the  two  circuits,  leaving  each 
complete  in  itself  for  simplex  operation.  Fig.  21  shows  the 
Weiny-Phillips  transmitter. 


Fig.  21. 


Normally,  when  both  the  eastern  and  western  circuits 
are  closed  at  the  distant  stations,  current  flows  through  all 
magnet  windings  of  the  repeater  set.  Thus,  normally, 


SIMPLEX  TELEGRAPHY  39 

current  flows  from  the  western  station  through  the  main- 
line coils  of  relay  R,  circuit-closing  switch  of  the  key  K, 
and  contact  y'  (which  is  closed)  of  the  transmitter  T",  to 
ground  at  G '.  Similarly,  current  flows  from  the  eastern 
station  through  R',  K' ',  and  y  to  G.  Both  relay  armatures 
are  therefore  attracted  and  keep  the.  transmitter  coils 
energized  through  the  batteries  B  and  B' '.  The  contacts 
x,  y  and  x',  y'  are  thus  normally  closed  and  currents  from 
the  batteries  BI  and  J52  flow  through  both  windings  of  the 
holding  coils.  Generators  are  very  frequently  used  instead 
of  batteries. 

When  the  western  operator  opens  the  circuit  preparatory 
to  signalling,  the  main-line  coils  of  relay  R  are  deprived  of 
current  and  the  armature  is  released,  inasmuch  as  the  hold- 
ing coil  //  exerts  no  attraction  due  to  the  neutralization  of 
magnetizing  forces  developed  in  the  two  windings.  This 
results  in  opening  the  circuit  of  the  magnet  of  transmitter 
T  and  the  release  of  its  armature.  The  positions  of  the 
moving  elements  of  the  instruments  at  this  instant  are  as 
shown  in  Fig.  19.  The  circuit  of  the  winding  bf  of  the 
holding  coil  Hf  is  broken  at  x  and  consequently  the  un- 
interrupted current  flowing  through  its  associate  winding 
a!  holds  the  tongue  of  relay  Rr  against  its  contact  stud 
irrespective  of  current  condition  in  the  main-line  coils. 
This  in  turn  maintains  current  flow  through  the  winding  of 
transmitter  T'  and  prevents  the  opening  of  the  western 
circuit  at  yr ,  and  the  opening  at  x'  of  coil  b  of  the  holding 
coil  H,  which  is  therefore  not  magnetized.  In  this  way 
the  continuity  of  the  western  circuit  is  preserved  at  the 
repeater  while  repeating  eastward.  A  moment  after 
breaking  the  circuit  at  x,  the  eastern  circuit  is  broken  at 
y  and  the  distant  relay  releases  its  armature. 


40  TELEGRAPH   ENGINEERING 

When  the  western  operator  depresses  his  key,  relay  R 
will  be  actuated,  and  then  the  transmitter  T  closes  the 
eastern  circuit  at  y,  which  is  followed  by  the  closing  of 
coil  bf  at  x.  The  distant  eastern  relay  is  thus  energized. 
Signalling  in  the  reverse  direction  is  accomplished  in  the 
same  manner. 

Atkinson  Repeater.  The  Atkinson  repeater  set  con- 
sists of  two  ordinary  relays  R  and  R',  two  transmitters  T 
and  Tf  similar  in  design  to  the  Weiny-Phillips  transmitters, 
and  two  repeating  sounders  S  and  S'  which  combine  the 
functions  of  relay  and  sounder,  the  connections  of  the  set 
being  shown  in  Fig.  22.  The  contacts  of  the  repeating 
sounders  are  shunted  across  the  corresponding  relay 
contacts. 

Normally,  when  no  messages  are  being  transmitted, 
the  windings  of  all  the  repeater  instruments  carry  current. 
Thus,  the  western  line  current  traverses  the  contact  x 
(which  is  closed)  of  the  transmitter  T  and  the  winding  of 
relay  R'  to  ground.  Similarly,  the  eastern  line  current 
traverses  x'  and  R  to  ground.  Both  relay  armatures  are 
therefore  in  contact  with  their  front  connecting  studs  and 
keep  the  transmitter  magnets  energized  by  means  of 
the  batteries  B  and  B' '.  The  contacts  y  and  y'  are 
thus  normally  closed  and  currents  from  the  batteries  b 
and  V  actuate  the  repeating  sounders  S  and  S'  respec- 
tively. 

When  the  western  operator  opens  the  key  prior  to  signal- 
ling, relay  R'  loses  its  magnetism  and  its  armature  falls 
back,  thereby  opening  the  circuit  of  the  magnet  of  trans- 
mitter Tfj  inasmuch  as  sounder  S'  remains  energized  and 
does  not  short-circuit  the  relay  contacts.  The  lever  of 
this  transmitter  first  opens  a  circuit  at  y'  and  immediately 


SIMPLEX  TELEGRAPHY  41 

afterward  opens  a  circuit  at  x'.  The  conditions  are  then 
as  shown  in  Fig.  22.  The  opening  of  the  circuit  at  yf 
causes  the  demagnetization  of  sounder  6*  and  the  release 
of  its  armature.  The  magnet  of  transmitter  T  will  thereby 
be  kept  energized  regardless  of  the  armature  position  of 
relay  R.  In  this  way  the  continuity  of  the  western  cir- 
cuit is  preserved  at  x.  The  circuit  opened  at  x'  is  the 
eastern  line  circuit.  Thus,  the  relay  at  the  eastern  station 


Fig.  22. 

releases  its  armature  as  the  distant  western  operator  opens 
the  circuit. 

As  this  operator  then  depresses  his  key,  relay  R'  is 
energized  and  its  armature  closes  the  transmitter  circuit 
at  T',  the  result  of  which  being  the  closing  of  the  eastern 
circuit  at  #',  followed  by  the  closing  of  the  circuit  of  re- 
peating sounder  S.  The  actuation  of  the  sounder,  how- 
ever, does  not  open  the  circuit  of  the  transmitter  magnet 
T,  because  the  relay  R,  energized  by  the  eastern  line 
battery  (not  shown)  at  the  closing  of  contacts  x',  keeps  its 
circuit  closed. 


42  TELEGRAPH   ENGINEERING 

Signalling  in  the  reverse  direction  can  be  traced  through 
the  repeater  in  the  same  manner. 

Other  Repeaters.  —  Many  other  closed-circuit  simplex 
repeaters  are  in  use,  among  which  may  be  mentioned  the 
Milliken,  Ghegan,  Horton,  Neilson  and  Toye  repeaters.*  f 
They  all  differ  in  the  methods  employed  to  prevent  one 
transmitter  breaking  the  circuit,  that  is  repeating  into  the 
other  circuit.  Repeaters  may  also  be  arranged  for  re- 
peating into  two  or  more  circuits;  the  Maver  multiple 
repeater*  is  one  of  this  type. 

For  the  satisfactory  operation  of  repeaters,  attendants, 
each  in  charge  of  a  certain  number  of  sets,  are  required  to 
supervise  the  working  of  the  repeaters  and  make  such  ad- 
justments as  are  necessary  to  maintain  uninterrupted 
service  despite  changes  in  weather  conditions  and  irregu- 
larities in  sending.  With  several  types  of  self-adjusting 
repeaters,  such  as  the  Catlin  and  D'Humy  repeaters,f  this 
supervision  may  be  dispensed  with. 

There  are  various  types  of  open-circuit  repeaters,  the 
simplest  of  which,  employing  only  two  double-contact  re- 


Fig.  23. 

lays,  is  represented  in  Fig.  23.  When  no  messages  are 
being  transmitted,  no  current  flows  through  the  line  wires 
and  repeater  relays,  and  consequently  both  relay  arma- 

*  For  description  see  Maver's  "American  Telegraphy." 
t  Described  in  McNicoPs  "  American  Telegraph  Practice." 


SIMPLEX  TELEGRAPHY  43 

tures  rest  against  their  upper  contact  studs.  When  the 
western  operator  depresses  his  key,  relay  Rf  attracts  its 
armature,  and  current,  supplied  by  battery  B',  flows  over. 
the  eastern  line.  At  the  same  time  the  magnet  circuit  of 
relay  R  is  broken  at  the  upper  contact  point  so  that  the 
continuity  of  the  western  circuit  remains  uninterrupted. 

PROBLEMS. 

1.  How  far  would  it  be  possible  to  telegraph  over  a  perfectly 
insulated  ground-return  line  having  8.36  ohms  resistance  per  mile  of 
length  with  an  impressed  voltage  of  1 20,  if  the  current  necessary  to 
actuate  the  two  75-ohm  relays  is  0.07  ampere? 

2.  How  many  gravity  cells,  each  having  a  voltage  of  i.o  and  an 
internal  resistance  of  2.5  ohms,  would  be  required  to  transmit  signals 
over  an  8o-mile  telegraph  line  which  has  a  resistance  of  5.28  ohms  per 
mile  and  is  equipped  with  two  i5o-ohm  relays  requiring  a  current  of 
0.04  ampere  ? 

3.  Three  relays  are  adjusted  to  operate  on  250  ampere- turns, 
and  have  the  following  constants: 

Relay  No.  i          20  ohms  resistance 2400  turns, 

Relay  No.  2          75  ohms  resistance 4500  turns, 

Relay  No.  3         150  ohms  resistance 7500  turns. 

If  these  relays  were  connected  in  series  across  2o-volt  mains,  which 
relays  would  operate  ?  What  voltage  would  cause  all  three  to  oper- 
ate? 

4.  What  is  the  best  winding  for  four  main-line  sounders  operating 
on  400  ampere-turns  when  used  on  a  telegraph  line  which  requires 
40  volts?    The  sounders  are  of  identical  construction  and  have  a 
winding  cross-section  of  0.9  square  inch  and  a  mean  length  of  turn 
of  2.2  inches;  double-cotton-insulated  wire  to  be  used,  the  insulating 
covering  being  four  mils  thick. 

5.  Over  how  long  a  line,  having  13.3  ohms  resistance  per  mile, 
could  the  four  sounders  of  the  preceding  problem  operate  when  the 
impressed  voltage  is  40  volts  ? 

6.  Four  separate  telegraph  lines,  each  having  a  total  resistance  of 
1000  ohms  including  receiving  instruments,  are  supplied  with  cur- 
rent by  one  battery  of  100  gravity  cells,  which  has  an  internal  re- 


44  TELEGRAPH   ENGINEERING 

sistance  of  220  ohms.  Determine  the  current  strength  in  a  circuit 
when  only  one  circuit  is  closed  and  also  when  all  four  circuits  are 
closed. 

7.  Decipher  the  following  message: 


8.  What  would  be  the  costs  per  mile  of  two  telegraph  lines  of 
standard  sizes  having  approximately  10.5  ohms  resistance  per  mile, 
one  constructed  of  galvanized  iron  and  the  other  of  hard-drawn 
copper  wire?    The  costs  of  iron  and  copper  may  be  taken  as  4^  and 
1 6  cents  per  pound  respectively. 

9.  A  4oo-mile  No.  6  B.  W.  G.  aerial  iron  line,  having  a  25o-ohm 
relay  and  a  120- volt  generator  at  each  end,  shows  an  insulation  re- 
sistance of  i  megohm  per  mile  in  wet  weather.     What  currents  flow 
through  one  relay  when  the  key  at  the  other  station  is  open  and 
when  closed? 

10.  Calculate  the  maximum  permissible  length  of  a  No.  10  B.  &  S. 
copper  telegraph  line  having  six  25o-ohm  relays  which  are  adjusted 
to  operate  on  0.05  ampere  and  release  on  0.025  ampere,  if   the  in- 
sulation resistance  of  the  line  be  taken  as  \  megohm  per  mile.    'Com- 
pute the  proper  voltage  to  be  impressed  at  each  end. 

11.  If  the  speed  of  telegraphic'  signalling  over  a  loo-mile  cable 
of  No.  1 6  B.  &  S.  copper,  having  a  capacity  of  0.12  microfarad  per 
mile,  is  200  five-letter  code  words  per  minute,  what  would  be  the 
possible  signalling  speed  over  a  6o-mile  cable  of  No.  19  B.  &  S.  wire 
having  a  capacity  of  o.n  microfarad  per  mile? 


CHAPTER   II 

DUPLEX  TELEGRAPHY 

i .  Duplex  Telegraph  Systems.  —  By  duplex  signalling 
is  meant  the  simultaneous  transmission  of  signals  in  oppo- 
site directions  without  interference  over  a  single  line. 
Four  operators  are  required  for  each  duplex  circuit,  one 
sending  and  one  receiving  operator  at  each  station.  The 
message  capacity  of  a  duplexed  line  is  therefore  twice  that 
of  the  same  line  when  operated  simplex.  When  telegraphic 
traffic  over  a  given  line  exceeds  that  which  can  be  handled 
satisfactorily  by  simplex  signalling,  it  is  advisable  to  install 
the  necessary  apparatus  at  the  terminal  stations  for  duplex 
signalling,  thereby  avoiding  the  expense  of  erecting  another 
line.  Duplex  telegraphy  was  first  performed  in  1853  by 
Dr.  Wm.  Gintl;  its  practical  operation  began  about  1868. 

Duplex  circuits  do  not  permit  of  the  intromission  of  inter- 
mediate stations,  but.  repeating  stations  may  be  inserted 
on  long  duplex  lines.  In  telegraph  systems  intended  for 
duplex  signalling,  the  receiving  instruments  at  both  sta- 
tions must  be  in  circuit  at  all  times  ready  to  respond  to 
signals  sent  from  the  distant  station,  and  yet  so  designed 
that  the  receiving  instrument  at  each  station  will  not 
respond  to  signals  sent  by  that  station.  These  condi- 
tions are  met  in  various  ways  in  the  different  duplex 
systems. 

There  are  three  systems  of  duplex  telegraphy:  the  dif- 
ferential duplex,  the  polar  duplex  and  the  bridge  duplex 

45 


46 


TELEGRAPH  ENGINEERING 


systems.*  The  first  system,  although  now  infrequently  used 
for  duplex  signalling,  is  an  essential  part  of  the  quadruplex 
telegraph  system  to  be  described  in  the  next  chapter,  and 
consequently  will  be  here  discussed.  Where  it  is  advis- 
able to  employ  a  battery  at  one  end  of  the  line  only,  a 
combination  of  the  differential  and  polar  duplex  systems 
may  be  used  for  duplex  operation  over  short  distances. 

2.  The  Differential  Duplex. — The  differential  duplex, 
also  known  as  the  single-current  duplex  and  as  the  Stearns 
duplex,  utilizes  a  differential  relay  as  the  receiving  instru- 
ment. This  is  a  relay  with  two  windings,  identical  as  to 
number  of  turns  and  resistance,  through  which  currents 


G' 


Fig.  x. 


may  flow  in  the  same  or  in  opposite  directions  around  its 
iron  cores.  The  corresponding  turns  of  the  windings  are 
preferably  wound  side  by  side  so  as  to  avoid  the  formation 
of  consequent  magnetic  poles.  For  clearness  in  diagrams, 
however,  these  windings  will  be  shown  as  being  adjacent. 
The  scheme  of  connections  of  the  differential  duplex  is 
represented  in  Fig.  i,  which  shows  a  line  L  extending  be- 
tween the  two  stations  A  and  B,  having  a  ground  return 

*  Early  duplex  schemes  are  described  in  Prescott's  "  Electricity  and  the 
Electric  Telegraph." 


DUPLEX  TELEGRAPHY  47 

path.  The  relays  R  and  Rr  have  two  windings  each  (a,  b 
and  a' ,  b'),  the  common  terminal  being  joined  to  the  levers 
of  keys  K  and  Kr  respectively.  The  similar  batteries 
B  and  Bf  are  connected  with  like  poles  to  the  front  con- 
tacts of  the  keys,  while  resistance  coils  d  and  d> ',  having  a 
resistance  equal  to  the  internal  battery  resistance,  are  con- 
nected to  the  rear  key  contacts.  In  this  way  the  resistance 
of  the  circuit  is  unaltered  whether  the  keys  are  on  the  front 
or  the  rear  contacts.  The  resistance  coil  r  is  adjusted  to 
have  a  resistance  equal  to  that  of  the  line  xy  plus  the 
resistance  from  the  point  y  to  ground  at  G'  and  the  ground 
resistance  G'  to  G,  and  similarly  the  coil  r'  to  have  a  re- 
sistance equal  to  that  of  the  line  plus  that  from  the  point 
x  to  ground  at  G  and  back  to  G'  (the  ground  resistance 
being  usually  neglected).  With  this  adjustment,  if  a  cur- 
rent enter  either  relay  at  the  junction  of  its  two  coils,  it 
would  divide  equally  between  the  two  paths  to  ground 
presented  to  it,  each  path  including  one  of  the  relay  coils. 
The  equal  components  of  this  current  in  the  two  coils 
circulate  around  the  core  in  opposite  directions  and 
consequently  the  magnetomotive  force  developed  by  one 
is  neutralized  by  that  developed  by  the  other,  thereby 
exerting  no  attractive  force  on  the  relay  armature. 

The  resistances  of  the  coils  r  and  r'  are  experimentally 
adjusted  in  practice  so  that  the  home  relay  is  not  affected 
by  movements  of  the  keys.  The  resistances  may,  however, 
be  determined  as  follows:  The  resistances  of  the  two  bat- 
teries will  be  assumed  equal  and  of  value  Rb  ohms  each," 
the  resistances  of  the  two  relays  likewise  of  Rr  ohms  each; 
then  from  the  symmetry  of  the  circuit  the  two  coils  r 
and  r'  will  also  have  equal  resistance,  say  r  ohms.  The 
line  will  be  assumed  perfectly  insulated  from  ground  and 


48  TELEGRAPH   ENGINEERING 

of  resistance  Rl  ohms.  For  exact  neutralization  of  mag- 
netizing forces  in  the  two  relays,  the  resistance  of  the 
one  path, 

f  +  r  +  *  (i) 

must  equal  that  of  the  other  path,  which  is 


2  _!_  I 

*    & 

2 


+  ^  +  r)  =  R,  (^  +  r  ) 


Whence 


(r>  2          1?    i;>7\ 
#r#6  +  RbRl  +  ^  +  £42]  =  o. 
4  2     / 

Therefore  the  resistance  of  each  coil  is 


r  =  —  +  -  V(Rl+Rr)(Rl+Rr  +  4R*).        (3) 

2          2 

Thus,  if  2oo-ohm  relays  are  connected  to  the  ends  of  a 
20oo-ohm  line  and  if  a  2oo-volt  gravity  battery  having  250 
ohms  internal  resistance  be  employed  at  each  end,  then 
the  resistance  coils  r  and  r'  would  each  have  a  resistance  of 


_  2  OOP 


+  -  V(20oo  +  200)  (2000  +  200  +  4  X  250) 


2  2 

=  2327  ohms. 

These  values  are  indicated  in  Fig.  2,  and  it  may  be  verified 
that  the  resistances  of  the  four  paths:  m,  n,  p,  m  —  (2,  pt 
m,  q,  Gf — G',  /,  q,  m,  G — g,  s,  t,  q,  are  all  equal  and  have  a 
resistance  of  2677  ohms. 


DUPLEX  TELEGRAPHY  49 

An  inspection  of  Fig.  i  will  reveal  the  principle  of  opera- 
tion of  this  system.  If  neither  key  be  depressed,  no  cir- 
cuit containing  an  E.M.F.  is  closed  and  therefore  no  relay 
is  actuated.  The  depression  of  only  one  key  at  either 
station  will  fail  to  actuate  the  relay  at  that  station  because 
of  equal  and  oppositely  directed  currents  in  the  halves  of 


100    -J-     100 


Rj  =  260 


Fig.  2. 

its  relay  coils,  but  will  actuate  the  relay  at  the  remote  sta- 
tion because  of  the  additive  action  of  these  currents.  The 
depression  of  both  keys  connects  both  batteries  in  opposi- 
tion and,  since  no  current  then  flows  in  the  line  wire  nor  in 
the  line  coils  b,  af,  of  the  relays,  both  relays  are  actuated 
by  the  currents  flowing  in  their  other  coils.  Although  a 
key  has  no  control  over  the  home  relay,  it  will  be  ob- 
served that  when  both  keys  are  depressed  each  relay  is 
operated  by  current  from  the  home  battery. 

Thus  in  this  system  a  relay  is  properly  actuated  when- 
ever the  key  at  the  other  station  is  depressed  regardless  of 
the  position  of  the  other  key. 

In  the  numerical  illustration,  the  steady  currents  in 
milliamperes  traversing  the  relay  coils  under  the  various 
conditions,  are  readily  seen  to  be  those  given  in  the  follow- 
ing table.  The  figures  following  the  braces  give  the 
equivalent  currents  through  one  coil  and  the  stars  indicate 
the  operation  of  the  relays. 


TELEGRAPH   ENGINEERING 


CURRENTS  IN   RELAY  COILS 


Relay 

Coil 

Neither 
key  de- 
pressed 

Key  K  only 
depressed 

Both  keys 
depressed 

Key  K'  only 
depressed 

R 

a 
b 

j| 

si? 

7*}75* 

JJ* 

R' 

a' 
b' 

o|° 

11  *• 

IS* 

21* 

In  the  manipulation  of  the  two  keys  as  shown,  there  are 
constantly  recurring  intervals  during  which  the  key  levers 
are  in  an  intermediate  position,  touching  neither  contact 
stud.  This  condition  is  apt  to  cause  confusion  of  signals, 
especially  on  leaky  lines.  In  differential  duplex  circuits 
where  primary  cells  are  used,  this  confusion  of  signals  may 
be  avoided  by  the  employment  of  transmitters  so  designed 
that  contact  is  made  with  one  stud  an  instant  before  con- 
tact is  broken  with  the  other.  The  appearance  of  such 
continuity- preserving  transmitters,  operated  magnetically  by 
means  of  a  local  circuit,  is  shown  in  Fig.  3. 


Fig.  3. 


The  connections  of  one  station  of  a  duplex  circuit  using 
this  transmitter,  are  shown  in  Fig.  4,  wherein  T  is  the 
transmitter,  and  j  and  k  are  the  contact  studs,  the  other 


DUPLEX   TELEGRAPHY 


letters  having  the  same  significance  as  before.  The  trans- 
mitter has  an  auxiliary  spring  lever,  insulated  from  the 
main  lever,  which  may  make  contact  either  with  the  fixed 


study  or  with  the  stud  k  attached  to  the  main  lever.  When 
the  key  is  depressed  the  contact  aty  is  made  before  that  at 
k  is  broken,  and  when  the  key  is  released,  the  contact  at  k 
is  made  before  that  aty  is  broken.  In  this  way  the  circuit 
from  m  to  ground  is  always  complete.  The  momentary 
short-circuits  of  the  line  battery  during  the  excursions  of 
the  transmitter  lever  do  not  prove  injurious  to  the  battery. 

3.  Artificial  Lines.  —  The  resistances  r  and  r'  of  Fig.  i, 
each  possessing  a  resistance  equal  to  that  of  the  line  plus 
that  of  the  terminal  apparatus  at  the  remote  station,  are 
aptly  termed  artificial  lines.  But,  since  actual  telegraph 
lines  have  electrostatic  capacity  with  respect  to  ground, 
for  more  exact  imitation  the  artificial  lines  should  also 
have  capacity.  When  the  artificial  line  has  the  same 
capacity  as  the  line  wire,  then  the  currents  through  them 
and  through  the  relay  coils  will  rise  and  fall  at  the  same 
rate.  That  this  result  is  essential  is  evident  from  the  fact 


TELEGRAPH   ENGINEERING 


that  if  the  current  should  rise  more  quickly  to  its  ultimate 
value  or  decay  more  rapidly  to  zero  in  one  relay  coil  than 
in  its  companion  coil,  the  armature  would  give  a  momen- 
tary kick  and  produce  a  false  signal  upon  each  depression 
or  release  of  the  home  key.  When  the  resistance  and 
capacity  of  the  artificial  line  in  a  duplex  circuit  are  so 
adjusted  that  the  depression  of  a  key  produces  no  effect 
upon  the  home  relay,  the  circuit  is  said  to  be  balanced. 

The  arrangement  of  an  artificial  line  which  is  used  by 
the  Postal  Telegraph-Cable  Company  for  duplex  telegraphic 


Fig-  5- 


signalling  is  given  in  Fig.  5.  The  resistance  between  the 
terminals  A  and  B  can  be  varied  from  10  to  11,100  ohms, 
and  each  of  the  two  condenser  sets  can  be  adjusted  from  o.i 
to  3.0  microfarads.  This  wide  adjustment  permits  of  its 
use  on  lines  of  different  lengths,  resistances  and  capacities. 
Parts  of  the  400-  and  i6oo-ohm  resistances  are  connected  in 
series  with  the  two  condenser  sets  in  order  to  vary  the  time 
of  their  charge  and  discharge  to  approximate  the  cor- 
responding times  for  the  line. 
The  design  of  the  Western  Union  artificial  line  is  shown 


DUPLEX   TELEGRAPHY 


53 


in  Fig.  6.  The  resistance  between  the  terminals  "  Ground" 
and  " Relay"  can  be  varied  from  25  up  to  11,000  ohms, 
and  each  of  the  two  condenser  sets  can  be  adjusted  from 
i  to  3!  microfarads.  One  of  the  resistances  connected  in 
series  with  the  condensers  can  be  varied  from  100  to  500 


10  W|  lyi  i  i     l  MI  i  i«i  i 


*    X 


1         2         |         2         I        J$        X        Ji 

Fig.  6. 

ohms  while  the  other  adds  from  200  to  1000  ohms.  When 
a  line  becomes  leaky  in  wet  weather,  the  resistance  of  its 
artificial  lines  must  be  lowered  for  balance. 

4.  Polarized  Relays.  —  The  polar  duplex  telegraph 
system  depends  for  its  operation  upon  reversals  in  the 
direction  of  current  flow.  In  this  system,  the  function  of 
the  key  is  not  to  make  and  break  the  circuit  as  in  the 


54 


TELEGRAPH   ENGINEERING 


Stearns  duplex,  but  instead  to  present  alternately  the 
positive  and  negative  poles  of  the  battery  to  the  line. 
Obviously  the  receiving  instrument  employed  must  oper- 
ate upon  current  reversals,  and  such  an  instrument  is 
called  a  polarized  relay. 

The  principle  of  the  simple  polarized  relay  may  be  ex- 
plained with  the  aid  of  Fig.  7.  A  U-shaped  permanent 
magnet  magnetized  to  have  two  equal  South  poles  as  indi- 
cated at  (a)  has  pivoted  at  its  mid-point  a  soft  iron  arma- 
ture which  projects  upward  and  plays  between  two  pole 
pieces  that  are  attached  to  the  ends  of  the  magnet,  as 
shown  at  (b).  The  North  magnetic  pole  is  then  shifted 
to  the  position  shown,  and  it  is  evident  that  the  armature 


SL 


(a) 


(6) 


s",LUn 
W) 


Fig.  7. 


will  remain  against  whichever  pole  piece  it  is  placed,  for  no 
retractile  spring  is  used.  A  winding  surrounds  each  pole 
piece  and  the  two  windings  are  connected  in  series.  Re- 
membering that  a  current  traversing  a  winding  around  an 
iron  core  will  cause  the  formation  of  magnetic  poles  as 
shown  at  (d),  it  will  be  evident  that  if  a  current  traverses 
the  windings  as  indicated  by  the  arrows  at  (c)  the  mag- 
netization due  to  the  permanent  magnet  in  the  left-hand 
pole  piece  will  be  partially  neutralized  while  that  in  the 
other  pole  piece  will  be  strengthened.  Consequently  the 
armature  will  be  drawn  over  toward  the  stronger  right- 
hand  pole  piece,  and  make  contact  with  the  right  contact 


DUPLEX  TELEGRAPHY 


55 


screw.  If  the  direction  of  current  flow  be  reversed,  the 
left-hand  pole  piece  will  be  the  stronger  and  therefore  the 
armature  will  make  contact  with  the  left-hand  contact 
stud.  Thus,  every  time  the  direction  of  current  changes, 
the  armature  will  move  from  one  contact  screw  to  the 
other. 

The  windings  of  the  polarized  relay  may  also  be  wound 
differentially  in  the  same  way  as  with  the  ordinary  or  neu- 
tral differential  relays,  already  described. 
Each  coil  contains  an  equal  number  of 
turns  belonging  to  the  two  windings.  To 
avoid  complicated  diagrams,  differentially- 
wound  relays  will  be  represented  as  in 
Fig.  8,  with  a  tap  m  at  the  middle  point 
of  the  winding.  When  current  is  sent  through  the  coils 
differentially  in  either  direction  the  armature  will  not  move 
from  the  position  previously  assumed. 


Fig.  8. 


Fig.  9. 

Fig.  9  shows  one  form  of  differentially-wound  polarized 
relay.    The  armature  is  pivoted  in  a  brass  casing  just 


TELEGRAPH  ENGINEERING 


below  the  upper  end  of  the  semicircular-shaped  permanent 
magnet  and  extends  between  the  adjustable  pole  pieces  of 
the  electromagnet  coils  that  are  mounted  on  the  other  end 
of  the  permanent  magnet.  The  post  supporting  the  con- 
tact points  is  shown  at  the  left. 

In  practice  polarized  relays  usually  have  resistances  of 
from  50  to  500  ohms,  and  will  operate  satisfactorily  on 
currents  of  from  5  to  200  milliamperes.  When  traversed 
by  currents  of  from  10  to  15  milliamperes,  the  inductances 
of  such  relays  are  from  1.5  to  6  henrys  when  the  air  gap 
between  armature  and  pole  faces  is  about  0.02  inch. 

5.  The  Polar  Duplex.  —  The  connections  of  the  ap- 
paratus used  on  a  polar  duplex  line  for  primary  battery 
operation  are  shown  in  Fig.  10.  The  pole-changing  trans- 


Fig.  10. 

mitters,  represented  by  C  and  C',  consist  of  double  arma- 
ture relays,  each  armature  playing  between  two  contact 
studs.  When  the  key  K  is  not  depressed,  retractile  springs 
hold  the  armatures  x  and  y  respectively  in  contact  with 
the  positive  and  negative  terminals  of  the  battery  B,  but 
when  the  key  is  depressed  the  armatures  are  attracted 


DUPLEX  TELEGRAPHY  57 

and  x  and  y  are  respectively  in  contact  with  the  negative 
and  positive  poles  of  the  battery.  In  other  words,  depres- 
sion of  the  key  reverses  the  polarity  of  the  home  battery 
with  respect  to  the  circuit. 

The  differentially-wound  polarized  relays  are  shown  at 
P  and  Pf  and  control  the  operation  of  the  local  sounders 
S  and  Sr  respectively.  The  letters  5  and  n  on  the  relay 
poles  represent  the  South  and  North  poles  due  to  the 
permanent  magnets  alone.  The  properly-balanced  arti- 
ficial lines  are  shown  at  AL.  The  proper  resistance  of 
the  artificial  line  may  be  calculated  similarly  to  the  method 
given  in  §  2. 

When  both  keys  are  open,  it  is  seen  that  the  negative 
terminals  of  both  main  batteries  are  connected  to  the 
mid-points  of  the  relay  windings,  and  that  therefore  no 
current  traverses  the  line  coils  a,  ai  and  e,  ei  of  the  relays. 
Currents,  however,  will  flow  in  the  artificial  line  coils  6,  61 
and  /,  /i,  and  these  are  in  such  direction  as  to  strengthen 
the  left-hand  poles  of  the  polarized  relays  and  weaken  their 
right-hand  poles,  and  consequently  both  armatures  will 
be  drawn  to  the  left  and  away  from  the  sounder  contacts. 
Hence  both  sounders  are  idle  when  both  keys  are  open. 

If  only  key  K  be  depressed,  the  positive  pole  of  battery 
B  is  connected  to  the  line  and  the  conditions  are  exactly 
as  represented  in  the  figure.  About  twice  as  much  cur- 
rent flows  through  the  line  coils  of  the  relays  as  through 
the  artificial  line  coils,  so  that  the  operation  of  the  relays 
depends  upon  the  direction  of  current  in  the  line  coils. 
The  current  in  the  coils  a  and  a\  strengthens  the  left-hand 
pole  and  weakens  the  right-hand  pole  of  relay  P}  and  con- 
sequently the  armature  stays  away  from  its  sounder  con- 
tact. At  the  other  station  the  current  in  the  line  coils 


58  TELEGRAPH  ENGINEERING 

e  and  e\  strengthens  the  right-hand  pole  and  weakens  the 
left-hand  pole  of  relay  P',  and  therefore  the  armature 
closes  the  local  circuit  and  the  sounder  S'  responds.  In 
like  manner  the  depression  of  key  K'  only  will  operate 
the  sounder  S.  Thus,  the  manipulation  of  one  key 
controls  the  operation  of  the  distant  sounder,  but  does  not 
control  the  home  sounder. 

When  both  keys  are  simultaneously  closed,  no  current 
again  flows  over  the  line,  because  the  positive  poles  of 
both  batteries  are  in  contact  with  the  line.  The  currents 
in  the  artificial  line  coils  are  now  in  such  a  direction  as  to 
weaken  the  left-hand  poles  and  strengthen  the  right-hand 
poles  of  both  relays.  Both  armatures  are  then  held  against 
the  local  circuit  contacts  and  both  sounders  operate.  In 
this  way  signalling  can  be  carried  on  in  opposite  directions 
over  a  single  wire.  If  relays  are  used  that  have  their 
armatures  magnetized  South,  reversal  of  the  batteries  will 
cause  the  system  to  operate  in  the  same  way. 

Continuity-preserving  pole-changers  may  be  used  with 
polar  duplex  systems  if  current  is  supplied  by  primary 
batteries,  but  their  use  is  not  so  important  as  the  use  of 
continuity-preserving  transmitters  with  differential  duplex 
systems.  For,  assume  key  K  to  be  depressed  while  key  K' 
is  open,  and  consider  the  instant  when  the  armatures  of 
the  pole-changer  C  are  midway  between  their  contacts. 
The  battery  B  is  then  completely  cut  off  from  the  circuit 
and  the  line  circuit  is  completed  to  ground  at  G  only 
through  all  coils  of  the  relay  P  and  the  artificial  line.  The 
line  current  from  battery  B'  flowing  through  these  coils  of 
the  home  relay  strengthens  the  left-hand  pole  and  weakens 
the  right  so  that  sounder  S  does  not  operate.  At  the  other 
station  more  current  traverses  the  coils  /,  /i  than  the  coils 


DUPLEX  TELEGRAPHY  59 

e,  e\  and  consequently  the  left-hand  pole  of  relay  Pf  is 
strengthened  and  the  other  is  weakened,  so  that  sounder  Sf 
is  not  operated  until  the  armatures  of  the  distant  pole- 
changer  touch  their  front  contacts.  Conversely,  sounder 
S'  will  release  its  armature  at  the  instant  when  armatures 
x  and  y  leave  their  front  contacts.  Again,  assume  that  key 
K  is  held  down,  as  in  Fig.  10,  which  means  that  the  relay 
armatures  of  P  and  P'  are  respectively  on  their  left  and 
right  contact  studs,  and  that  sounder  5"  is  actuated.  If 
now  key  Kf  is  also  depressed  the  pole-changer  C'  operates, 
and  its  armatures  will  be  drawn  toward  their  front  stops. 
Consider  the  instant  when  these  armatures  are  in  their 
intermediate  positions,  touching  neither  contacts.  The 
battery  Bf  is  then  completely  isolated,  and  the  only  path 
for  the  line  current  at  station  B  is  through  all  four  coils 
of  relay  P'  and  through  the  artificial  line  to  ground  at  G '. 
The  current  supplied  by  battery  B  enters  the  relay  P  at 
junction  y  and  divides  between  the  line  and  artificial  line 
coils.  The  current  through  the  coils  of  relay  P'  keeps  the 
right-hand  pole  magnetized  stronger  than  the  left  so  that 
sounder  Sf  will  remain  actuated.  At  the  other  station 
more  current  flows  through  the  coils  b  and  b\  than  through 
the  others,  and  is  in  such  direction  as  to  magnetize  the 
right-hand  pole  stronger  than  the  left  and  consequently 
the  sounder  S  will  operate  as  soon  as  the  armatures  x'  and 
y'  leave  their  rear  contacts.  Conversely,  sounder  5  will 
remain  actuated  until  these  armatures  again  touch  their 
rear  contacts.  Thus  false  signals  can  hardly  ensue  with 
the  polar  duplex  if  properly  balanced. 

A  polar  duplex  circuit  is  balanced  in  practice  by  first 
adjusting  the  polarized  relays,  with  all  current  cut  off,  so 
that  the  armatures  will  move  with  equal  force  from  their 


60  TELEGRAPH   ENGINEERING 

intermediate  positions  to  either  stop  and  remain  there. 
Then  connect  the  relays  in  circuit.  At  one  station  alter- 
nately depress  and  release  the  key  while  varying  the  re- 
sistance of  the  artificial  line  until  such  manipulation  of  the 
key  does  not  alter  the  behavior  of  the  home  relay.  The 
capacity  of  the  artificial  line  is  adjusted  by  first  moving 
back  that  magnet  pole  piece  which  is  on  the  side  away 
from  the  local  circuit  contact,  and  then,  starting  with  all 
the  condensers  in  circuit,  gradually  diminish  the  capacity 
and  alter  the  resistances  in  series  with  the  condensers, 
while  depressing  and  releasing  the  key  at  intervals,  until 
the  relay  armature  will  not  kick  with  every  movement  of 
the  key.  This  adjustment  signifies  that  the  current  grows 
and  decays  simultaneously  in  both  relay  windings.  Then 
restore  the  pole  piece  to  its  proper  position,  and  the  balance 
is  complete.  The  other  station  is  adjusted  similarly. 

A  single-armature  pole-changer,  such  as  illustrated  in 
Fig.  n,  is  extensively  used  with  duplex  telegraph  circuits 


Fig.  ii. 

when  operated  by  generators.  The  armature  moves  be- 
tween two  contacts,  one  being  connected  to  the  positive 
terminal  of  one  generator  and  the  other  contact  to  the 
negative  terminal  of  another  similar  generator,  the  two 


DUPLEX   TELEGRAPHY 


6l 


other  generator  terminals  being  grounded  as  shown  in 
Fig.  12.  Another  generator  supplies  current  to  the  local 
pole-changer  circuit.  The  same  generators  may  furnish 


Fig.  12. 

current  to  other  duplex  circuits,  by  connecting  these  cir- 
cuits, each  with  protective  fuses,  /,  /,  /,  to  the  positive  and 
negative  bus-bars. 

This  figure  shows  the  transmitting  arrangement  used  by 
the  Postal  Telegraph-Cable  Company.  At  the  instant  of 
transferring  contact  from  one  stud  to  the  other  a  spark  is 
produced  and  drawn  across  the  air  gap,  thereby  bridging 
the  two  2oo-volt  generators  through  the  3oo-ohm  protec- 
tive resistances.  These  resistances  (usually  in  lamp  form) 
protect  the  machines  in  cases  of  accidental  short-circuit. 
This  spark  is  effectively  quenched  by  the  provision  of  a 
discharge  path  to  ground  through  a  ^-microfarad  con- 
denser, for  each  machine,  as  shown.  Three-hundred  ohm 
or  6oo-ohm  protective  resistances  are  usually  connected  in 
series  with  the  generators. 

In  order  to  find  the  current  strength  in  the  various  por- 
tions of  a  polar  duplex  circuit  let  Rp,  Rb,  Rl  and  r  be  re- 
spectively the  resistances  of  the  polarized  relays,  battery  or 
protective  resistance  in  series  with  generator,  perfectly  in- 


62  TELEGRAPH   ENGINEERING 

sulated  line,  and  artificial  line,  let  7,  7i  and  72  be  respectively 
the  current  supplied  by  each  battery  or  generator,  current 
in  artificial  line  and  current  in  line  wire,  and  let  E  be  the 
voltage  of  each  battery  or  generator.  Then,  when  both 
keys  are  open  or  both  closed 

•p 
I  =  I\  =  =  -  and  72  =  o;  (4) 


2 

when  one  key  is  closed 

E-RJ  2  (E  -  RJ) 


,. 

2,       (5) 


2 


E  (2  Rp  +  Rl  +  2  r) 
whence    7  =  -  —    — 

4- 


In  order  to  have  72  twice  as  great  as  I\,  the  artificial  lines 

•p 
should  have  a  resistance  of  r  =  —  2  +  -K/. 

2 

Where  only  generators  of  higher  voltage  are  in  service, 
as  necessary  for  the  operation  of  long  quadruplex  telegraph 
circuits  (see  next  chapter),  the  potential  may  be  reduced 
to  values  sufficient  for  duplex  operation  by  the  intro- 
duction of  a  leakage  path  to  ground.  The  connections  of 
one  station  of  such  a  leak  duplex  circuit,  as  used  by  the 
Postal  Telegraph-Cable  Company,  are  shown  in  Fig.  13. 
Fourteen-hundred-ohm  resistances  are  in  series  with  the 
generators,  and  22oo-ohm  shunt  or  leak  paths  are  provided 
to  ground.  The  difference  of  potential  between  the  point 


y  and  ground  does  not  exceed  -  -  X  380  or  233 

1400  +  2200 

volts  and  this  occurs  when  the  armature  is  midway  between 


DUPLEX  TELEGRAPHY 


the  pole-changer  contacts.     Assuming  that  each  winding  of 
the  polarized  relay  has  a  resistance  of  150  ohms  and  that 


the  artificial  line  has  a  resistance  of  1700  ohms,  this  poten- 
tial difference  would  fall  to 


380  —  1400 


380 


or  159  volts, 


1400 


(1700  +  15°)  22QQ 

22OO  +  I7OO  +  150 

when  the  armature  makes  contact  so  that  no  current  flows 
over  the  line.  In  this  way  the  voltages  available  at  the 
pole-changer  contacts  are  rendered  materially  less  than  the 
terminal  voltages  of  the  generators. 

6.  Improved  Polar  Duplex.  —  The  arrangement  of  the 
improved  polar  duplex  circuit  due  to  Davis  and  Eaves  and 
now  employed  by  the  Postal  Telegraph  Company  is  shown 
in  Fig.  14.  The  principle  of  operation  is  identical  with 
that  already  described  in  connection  with  Fig.  10,  and  it 
will  be  observed  that  the  transmitting  arrangement  used 
is  that  of  Fig.  12.  The  additional  features  of  this  duplex 
circuit  are  the  resistances  g,  h,  j,  k,  I  and  m  and  the  con- 
densers c,  cf,  Ci  and  c^  the  functions  of  which  will  be  ex- 
plained presently. 

It  was  pointed  out  in  the  last  section  in  describing  the 
polar  duplex  circuit,  that  with  the  home  key  open,  (i)  the 


TELEGRAPH  ENGINEERING 


home  sounder  is  not  operated  until  the  distant  pole-changer 
armature  touches  its  front  contact  and  (2)  that  it  will 
cease  to  operate  at  the  instant  this  armature  leaves  this 
front  contact.  Also,  that  with  the  home  key  closed, 
(3)  the  home  sounder  will  operate  as  soon  as  the  distant 
pole-changer  armature  leaves  its  rear  contact  and  (4)  will 
remain  actuated  until  this  armature  again  touches  its  rear 
contact.  Thus,  conditions  2  and  3  permit  of  faster  trans- 
mission of  signals  than  the  others.  The  introduction  of 
the  non-inductive  resistances  g,  h,  j  and  k,  each  of  500- 
ohms  resistance  and  the  12 -microfarad  condensers  c  and  cf 


Fig.  14. 

is  for  the  purpose  of  quickening  transmission  for  the  slow 
conditions  (i)  and  (4). 

When  both  keys  are  open  the  negative  generator  termi- 
nals touch  armatures  y  and  yf  of  the  pole-changers  and  no 
current  traverses  the  line,  line  coils  of  both  relays,  or  re- 
sistances g  and  j.  Currents,  however,  flow  from  the  gen- 
erators tov  ground,  through  the  artificial  lines,  lower  relay 
windings  and  resistances  h  and  k  back  to  their  respective 
generators.  As  a  consequence  the  condensers  c  and  c'  will 
be  charged  respectively  to  the  potential  differences  exist- 
ing across  the  resistances  h  and  &,  the  plates  w  and  z  being 
charged  positively.  If,  now,  key  K  is  depressed,  the 
armature  y  of  pole-changer  C  travels  from  the  rear  to  the 
front  contact.  In  its  intermediate  position,  the  armature 


DUPLEX  TELEGRAPHY  65 

isolates  the  generators  D.  A  current  'now  flows  from  the 
generator  Df  to  ground,  through  the  left-hand  artificial  line, 
relay  P,  resistances  h  and  g,  line,  upper  coils  of  relay  P'  and 
resistance  j  back  to  the  generator;  and  this  current  is 
about  one-half  that  which  flows  from  the  same  generator 
through  the  right-hand  artificial  line,  lower  coils  of  relay 
Pr  and  resistance  k  back  to  the  generator.  The  charge  on 
condenser  c  remains  practically  unchanged  because  its 
potential  difference,  that  across  coils  g  and  h,  is  due  to  a 
current  of  approximately  half  the  initial  strength  though 
double  the  initial  resistance.  This  condenser  will  produce 
no  appreciable  discharge. 

At  the  other  station,  however,  the  potential  difference  of 
condenser  c'  is  now  that  across  coil  k  minus  that  across 
coil  7,  and  is  therefore  approximately  half  that  possessed 
before  and  in  the  same  sense.  This  condenser  will  then 
discharge  partially  and  a  current  pulse  flows  from  q  through 
the  lower  coils  of  relay  P',  both  artificial  lines,  relay  P, 
resistances  g  and  h,  line,  upper  coils  of  relay  Pf  to  the  other 
condenser  terminal  at  p.  This  current  does  not  affect  the 
relay  P,  but  it  does  tend  to  operate  the  relay  P'  momen- 
tarily. This  discharge  current  through  all  coils  of  P'  is  in 
the  same  direction  as  that  which  will  flow  through  its 
upper  coils  when  the  pole-changer  armature  y  reaches  the 
front  contact.  Thus  the  condenser  discharge  begins  the 
operation  of  the  home  relay  at  the  instant  the  distant 
pole-changer  armature  leaves  the  rear  contact,  and  this 
operation  is  completed  by  the  generators  as  this  armature 
reaches  its  front  contact.  The  improvement  for  the  fourth 
condition  can  be  traced  similarly. 

The  function  of  the  four  6oo-ohm  non-inductive  resist- 
ances /,  /',  m  and  m' ',  with  the  four  i-microfarad  condensers 


66 


TELEGRAPH  ENGINEERING 


Ci>  Ci,  £2  and  £2',  shunted  around  the  relays  is  to  provide  an 
auxiliary  path  to  ground,  for  inductive  'disturbances  from 
neighboring  telegraph,  telephone  or  high-tension  transmis- 
sion lines,  which  does  not  include  the  relay  windings,  thereby 
eliminating  such  interference  with  the  operation  of  the 
duplex  circuit.  The  shunt  circuits  offer  a  further  advantage 
in  that  the  first  portion  of  the  current  pulse  for  each 
signal  over  this  home  shunt  path  reaches  the  other  end  of 
the  line  a  little  in  advance  of  the  current  which  passes 
through  the  home  relay  windings.  This  action  assists  in 
attaining  a  high  signalling  speed. 

7.  Short-line  Duplex.  —  The  circuit  of  the  Morris 
duplex,  which  system  is  successfully  employed  by  the 
Western  Union  Telegraph  Company  on  many  short  lines, 
is  shown  in  Fig.  15.  It  utilizes  a  neutral  relay  at  one  sta- 


Fig.  15. 

tion  and  a  polarized  relay  at  the  other,  and  employs  main- 
line generators  at  one  station  only.  The  artificial  line  has 
a  resistance  equal  to  the  resistance  from  the  point  x  to 
ground  at  G '.  The  resistance  of  the  compensating  rheo- 
stat r\  is  adjusted  so  that  three  times  as  much  current  flows 
through  the  line  when  the  key  K'  is  depressed  as  when  Kf 
is  open.  These  conditions  are: 

r  =  SI  +  Rr  +  rlt  (7) 


DUPLEX  TELEGRAPHY  67 


where  Rp  and  .Rr  are  the  resistances  of  the  polarized  and 
differential  neutral  relays  respectively,  R^  is  the  resistance 
in  series  with  the  generator,  RL  is  the  resistance  of  the 
assumedly  perfectly-insulated  line  and  r  is  the  resistance 
of  the  artificial  line.  Thus,  if  Rl  =  1000  ohms,  Rb  =  300 
ohms,  Rr  =  200  ohms  and  Rp  =  400  ohms,  then 

r  =  ri  +  1400, 

600  (200  -f  2  r) 
ri=      800+  ,r 

whence  r  =  4966  ohms  and  r\  =  3566  ohms. 

The  function  of  the  repeating  sounder  RS  is  to  eliminate 
false  signals  when  key  K  is  depressed  while  the  other  key 
is  held  down.  The  reversal  in  magnetization  of  relay  R 
takes  place  quickly  and  before  its  armature  has  an  oppor- 
tunity to  fall  back  to  its  rear  contact  and  open  the  circuit 
of  sounder  S.  In  view  of  the  foregoing  descriptions,  the 
operation  of  this  duplex  system  may  be  readily  understood 
without  further  comment,  by  tracing  the  conditions  when 
no  keys,  either  of  the  two  keys,  and  both  keys  are  depressed. 

8.  The  Bridge  Duplex.  —  The  form  of  the  bridge  duplex 
circuit  resembles  that  of  the  Wheats  tone  bridge,  in  having 
four  arms  with  the  home  receiving  instrument  connected 
across  opposite  arm  junctions,  as  shown  in  Fig.  16.  For 
the  station  A  the  bridge  arms  are:  winding  a  of  the  re- 
tardation coil  /,  line  xy  plus  the  paths  from  y  to  ground  at 
the  right-hand  station,  artificial  line  A  LI,  and  the  winding  b 
of  the  same  retardation  coil.  The  arrangement  for  station 
B  is  identically  the  same.  The  simple  polarized  relays  are 


68 


TELEGRAPH  ENGINEERING 


connected  across  the  junctions  x,  w  and  y,  z.  The  artificial 
line  at  each  station  is  adjusted  to  equal  the  resistance  of 
the  line  and  the  apparatus  at  the  distant  station,  and  the 
resistances  of  the  two  coils  of  each  retardation  coil  are  equal. 
When  both  keys  are  idle,  the  armatures  of  the  pole- 
changers  C  and  C'  rest  against  their  rear  stops  which  are 
joined  to  the  positive  generator  terminals,  and  therefore 
no  current  traverses  the  line  wire.  At  station  A  a  current 
divides  at  the  point  m,  one  part  traversing  winding  a  and 
relay  P,  and  the  other  part  traversing  winding  bj  both 


Fig.  16. 

currents  then  combining  at  the  point  w  to  flow  through  the 
artificial  line  A  LI  to  ground  and  back  to  the  other  generator 
terminal;  while  at  station  B,  a  current  divides  at  the 
point  n,  one  part  traversing  winding  c  and  relay  P' ',  and 
the  other  part  traversing  winding  d,  both  currents  then 
combining  at  the  point  z  to  flow  through  the  artificial  line 
ALz  to  ground  and  back  to  the  other  generator  terminal. 
It  will  be  observed  that  the  direction  of  the  currents  through 
the  two  relays  is  such  that  the  relay  armatures  touch  their 
idle  contacts  and  therefore  do  not  close  tjie  local  sounder 
circuits,  as  indicated  in  the  figure. 

When  the  key  K  is  depressed,  the  armature  of  pole- 
changer  C  touches  the  negative  generator  terminal,  and 
consequently  more  current  flows  over  the  line  than  through 
either  artificial  line,  and  this  current  flows  from  y  to  x. 


DUPLEX  TELEGRAPHY  69 

The  line  current  entering  at  the  point  y  is  made  up  of  the 
current  coming  through  the  coil  c  and  that  coming  from  z 
through  the  relay  Pf .  The  direction  of  this  current  is 
such  that  the  right-hand  pole  of  the  relay  will  be  more 
strongly  magnetized  than  the  left  and  consequently  its 
armature  closes  the  sounder  circuit.  At  station  A  the 
arriving  current  divides  at  the  point  x,  and  that  part 
which  traverses  the  relay  P  is  in  such  direction  as  to  mag- 
netize the  left-hand  pole  more  strongly  than  the  right,  so 
that  this  relay  will  not  close  the  sounder  circuit.  Thus, 
the  depression  of  one  key  controls  the  operation  of  the 
distant  relay  and  sounder. 

If  both  keys  are  closed,  both  pole-changer  armatures 
will  be  in  contact  with  the  negative  generator  terminals, 
and  again  no  current  will  flow  over  the  line.  Currents  will 
now  flow  through  relay  P'  from  z  to  y,  and  through  relay 
P  from  w  to  x,  and  their  direction  is  such  as  to  magnetize 
the  right-hand  poles  stronger  than  the  others  and  con- 
sequently the  relay  armatures  will  close  both  sounder  cir- 
cuits. Although  each  relay  is  caused  to  operate  by  its 
home  battery,  yet  its  action  is  controlled  entirely  by  the 
distant  key. 

It  will  be  noted  that  each  receiving  instrument  is  always 
shunted,  so  that  only  a  part  of  the  generator  current  can 
flow  through  the  relay.  The  magnitudes  of  the  currents 
in  the  various  paths  can  best  be  compared  by  means  of  a 
numerical  illustration. 

Using  8oo-ohm  polarized  relays,  3oo-ohm  resistances  in 
series  with  each  generator,  and  retardation  coils  with  500 
ohms  resistance  per  winding,  at  the  ends  of  a  i  poo-ohm 
perfectly-insulated  line,  requires  that  the  artificial  lines  be 
adjusted  to  have  a  resistance  of  2500  ohms.  The  joint  re- 


70  TELEGRAPH  ENGINEERING 

sistance  of  the  paths  from  the  points  x  or  y  to  ground  at 
the  corresponding  station  is  then  600  ohms  (calculated 
according  to  equation  (9)  following);  thus  the  resistances 
of  the  artificial  lines  are  correct,  viz.  1900  +  600  =  2500 
ohms.  The  steady  currents,  in  milliamperes,  flowing 
through  these  paths  for  various  sending  conditions  with 
1 50- volt  generators,  are  given  in  the  following  table,  and 
their  directions  are  indicated  by  +  and  —  in  connection 

a  =  600  Rl  =   1900  C  =  500 


ffcov. 


Fig.  17- 

with  the  scheme  of  Fig.  17,  the  +  sign  signifying  a  cur- 
rent flowing  upwards  or  toward  the  right,  while  —  denotes 
a  current  flowing  downwards  or  toward  the  left.  The  stars 
represent  the  operation  of  relays. 

CURRENTS  IN   BRIDGE   DUPLEX  CIRCUIT 


3 

ft, 

fc 

a? 

Condition 

'a) 

s 

g 

I 

^ 

O 

c 

^ 

1 

a 

§ 

§ 

1 

ft 

$ 

Neither  key  depressed  

+48 

+13 

+35 

-13 

-48 

0 

-48 

-13 

-13 

-35 

+48 

Key  K  depressed      

—  120 

—71 

—  49 

—13 

_j_  ^ 

-81 

-tf 

+n* 

—71 

—  49 

+120 

Key  K'  depressed             

+120 

+71 

+  10 

+13* 

—36 

+81 

—13 

+7T 

+  10 

—  I2O 

Both  keys  depressed  .     ... 

-48 

-13 

-35 

+13* 

+48 

0 

+48 

+13* 

+13 

+35 

-48 

fBy  equation  (80)  of  Chap.  X. 


DUPLEX  TELEGRAPHY  71 

The  resistance  of  the  terminal  apparatus  when  a  =  b  is 
calculated  from  the  equation 

R  _  aP  (2  Rb  +  g)  +  RbAL  (2  a  +  P)  +  all  (a  +  P)      ,  , 


which  is  obtained  by  an  application  of  Kirchhoff's  laws. 
Since,  for  a  perfectly  insulated  line 

AL  =  Ro  +  Rl, 

by  combining  with  equation  (9)   there  results  that  the 
proper  resistance  of  the  artificial  line  should  be 


where     p  _*(«  +  2*») 


The  bridge-duplex  arrangement  used  by  the  Western 
Union  Telegraph  Company  embodies  various  improve- 
ments on  the  system  described,  and  will  now  be  considered. 

The  retardation  coil  comprises  two  5oo-ohm  coils  wound 
upon  a  circular  core  of  rectangular  cross-section,  made  up 
of  soft  iron  wires.  The  core  has  an  inside  diameter  of  3! 
inches,  an  outside  diameter  of  5!  inches,  and  is  if  inches 
wide;  it  is  composed  of  about  6000  turns  of  No.  26  B.  &  S. 
annealed  iron  wire.  Each  winding  has  7900  turns  of  No.  29 
B.  &  S.  double-cotton-covered  copper  wire  and  has  a  re- 
sistance of  about  400  ohms.  Its  resistance  is  brought  up 
to  500  ohms  by  adding  approximately  no  turns  of  No.  28 
german  silver  wire  wound  back  on  themselves,  to  render 
this  compensating  winding  non-inductive. 

Each  5oo-ohm  coil  possesses  considerable  inductance, 
and  consequently  a  current  coming  over  the  line  wire  meets 
at  first  with  great  opposition  in  traversing  the  retardation 


72  TELEGRAPH   ENGINEERING 

coil,  because  of  the  counter  electromotive  force  of  self-in- 
duction which  is  developed  in  it.  This  electromotive  force 
is  in  such  direction  as  to  assist  in  the  rapid  growth  of  cur- 
rent in  the  polar  relay  to  a  value  momentarily  greater 
than  the  steady  value.  This  initial  pulse  of  current 
through  the  relay  causes  its  armature  to  be  moved  from 
stop  to  stop  with  great  rapidity.  The  retardation  coils  do 
not  hinder  outgoing  currents  very  much  because  differing 
currents  pass  through  the  two  windings  of  the  coils  differ- 
entially, and  the  magnetism  developed  in  the  core  by  one 
winding  is  neutralized  to  some  extent  by  that  developed 
by  the  other,  and  hence  the  coils  for  this  condition  are  less 
inductive  than  before. 

In  order  that  the  speed  of  pole-changer  armatures  shall 
be.  high,  two  series-connected  electromagnets  are  provided 
on  each  instrument,  one  on  either  side  of  the  armature. 
The  iron  cores  of  the  front  magnet  are  laminated  while 
those  of  the  rear  magnet  are  solid  and  surrounded  by 
copper  sleeves,  thereby  causing  the  magnetism  to  be  es- 
tablished much  more  rapidly  in  the  front  than  in  the  rear 
magnets.  Light  retractile  springs  hold  the  armatures 
against  their  back  contacts  when  the  keys  are  elevated. 
When  the  key  is  depressed,  current  flows  through  both 
pole-changer  electromagnets,  but  the  armature  is  drawn 
toward  the  front  contact  because  sufficient  attraction  is 
first  exerted  by  the  front  magnet.  As  the  armature  is 
now  further  from  the  rear  magnet,  subsequent  full  magneti- 
zation of  this  magnet  cannot  cause  its  return.  However, 
when  the  key  is  released,  the  rear  magnet  retains  its  mag- 
netism much  longer  than  the  other,  and  consequently  the 
armature  is  brought  over  to  its  rear  contact  far  more 
rapidly  than  if  the  spring  alone  were  acting.  For  26-volt 


DUPLEX  TELEGRAPHY  73 

local-circuit  operation  each  electromagnet  has  a  resistance 
of  4  ohms,  while  for  52-volt  operation  each  has  13  ohms 
resistance. 

A  milliammeter,  reading  to  50  milliamperes  in  either 
direction,  is  placed  in  series  with  the  polarized  relays  to 
measure  the  current  flowing  and  to  facilitate  line  balancing. 
When  the  artificial  line  resistance  and  capacity  are  so  ad- 
justed that  the  milliammeter  needle  is  practically  unaffected 
by  the  manipulation  of  the  home  key,  a  good  working 
balance  is  established. 

For  increasing  the  resistance  of  short  lines  for  operation 
at  the  voltages  usually  employed  in  duplex  signalling,  a 
line-resistance  box  is  used  at  each  station.  It  contains 
two  separate  and  identical  sets  of  resistances  (five  25o-ohm 
resistances  in  each  set)  simultaneously  adjustable  by  means 
of  a  double  lever.  These  resistances  are  interposed  in  the 
real  and  artificial  lines  at  the  points  w,  x,  y  and  z,  Fig.  16. 
The  variation  of  each  line  resistance,  requires  an  adjust- 
ment of  the  distant  artificial  line.  The  insertion  of  this  re- 
sistance, which  is  almost  perfectly  insulated  from  ground, 
in  the  line  circuit  during  wet  weather,  raises  the  apparent 
insulation  of  the  whole  line,  that  is  the  insulation  resist- 
ance per  ohm  of  line  is  greater  than  before. 

The  method  of  quenching  the  sparks  produced  at  the 
pole-changer  contacts  is  similar  to  that  shown  in  Fig.  12, 
but  the  ground  connection  at  the  point  x  is  replaced  by  a 
2o-ohm  resistance  lamp  connected  in  series  with  the  con- 
densers; or  a  single  \  mf.  condenser  may  be  used  instead 
of  the  two  J  mf.  series-connected  condensers.  In  practice 
non -ad  jus  table  i  mf.  condensers  are  also  connected  to  the 
points  m  and  n  of  Fig.  16,  their  other  terminals  being 
grounded. 


74 


TELEGRAPH   ENGINEERING 


9.  Advantage  of  Double-current  Duplex  Systems.  —  It 
has  been  stated  that  the  differential  or  single-current 
duplex  is  infrequently  used  because  of  the  superiority  in 
practice  of  the  polar-  and  bridge-duplex  systems,  these 
latter  being  called  double-current  duplexes.  Considerable 
difficulty  is  experienced  in  maintaining  operation  over 
single-current  duplex  lines  when  the  weather  is  unfavor- 
able, because  the  line  insulation  is  poor.  That  this  is  the 
case  can  be  seen  from  the  following  illustration. 

In  §  2  a  474-mile,  2ooo-ohm  differential  duplex  line  with 
two  2oo-ohm  relays  was  considered.  A  2oo-volt  gravity 
battery  having  an  internal  resistance  of  250  ohms  and  a 
23  2 7 -ohm  artificial  line  was  employed  at  each  end.  The 


2827 


Fig.  18. 

table  in  that  section  shows  the  current  strengths  in  the 
relay  coils  when  the  line  is  perfectly  insulated.  If  the  in- 
sulation resistance  should  fall  to  i  megohm  per  mile,  and 
considering  the  distributed  leakage  to  be  concentrated  at 
the  middle  of  the  line,  the  conditions  are  representable  by 
Fig.  18. 

It  can  readily  be  verified  that  the  currents  then  travers- 
ing the  relay  coils,  under  otherwise  identical  conditions, 
will  be  as  shown  in  the  following  table.  The  figures  fol- 
lowing the  braces  give  the  equivalent  currents  through  one 
relay  coil. 


DUPLEX  TELEGRAPHY 


75 


CURRENTS  IN  NEUTRAL  RELAY  COILS,  EXPRESSED  IN 
MILLIAMPERES 


Relay 

R 

Coil 

Neither 
key  de- 
pressed 

Key  K  only 
depressed 

Both  keys 
depressed 

Key  K'  only 
depressed 

a 
b 

:l° 

SH 

III- 

Jfsr 

Rf 

a' 
b' 

:}° 

5sl" 

Z\*° 

SH 

To  assure  satisfactory  operation  under  these  conditions  the 
relays  must  be  adjusted  so  that  they  will  not  operate  on 
18  milliamperes  through  one  coil,  but  will  operate  on  40 
milliamperes.  For  longer  lines  or  for  poorer  insulation  this 
margin  of  22  milliamperes  will  be  reduced  and  operation 
rendered  unsatisfactory. 

Consider  a  polar  duplex  line  to  have  the  same  constants. 
When  this  line  is  perfectly  insulated,  the  currents  travers- 
ing the  relay  coils  are  as  tabulated  below,  the  values  being 
computed  in  accordance  with  equations  (4),  (5)  and  (6). 

CURRENTS  IN  POLARIZED  RELAY  COILS,  EXPRESSED  IN 
MILLIAMPERES 


Relay 

Coil 

Both  keys 
raised  or  de- 
pressed 

One  key  only 
depressed 

R 

a 
b 

7Sh 

ih« 

R' 

a' 
b' 

nfr 

•£}« 

When  the  line  is  poorly  insulated,  and  the  multitude  of 
leakage  paths  be  considered  grouped  at  the  middle  point  q 
of  the  line,  and  one  key  be  depressed,  this  point  q,  being 
midway  between  +  200  and  —  200  volts,  will  be  at  zero 
potential  with  respect  to  ground,  and  consequently  leak- 


76 


TELEGRAPH   ENGINEERING 


age  will  cause  no  alteration  in  current  distribution,  and  the 
current  values  in  the  last  column  still  apply.  The  follow- 
ing table  shows  the  currents  then  traversing  the  relay 
windings  for  all  key  positions.  A  margin  of  at  least  40 

CURRENTS  IN  POLARIZED   RELAY  COILS,   EXPRESSED  IN 
MILLIAMPERES 


Relay 

Coil 

Both  keys 
raised  or  de- 
pressed 

One  key  only 
depressed 

R 

a 
b 

Sir 

wf« 

R' 

a' 

b' 

f> 

"El" 

milliamperes  is  effective  for  operating  the  relays.  Of  course, 
if  these  leakage  paths  were  considered  uniformly  distrib- 
uted along  the  line,  the  tabulated  values  would  be  altered 
somewhat,  but  it  is  clear  that  the  double-current  duplex 
systems  are  not  as  sensitive  to  weather  variations  as  is  the 
single-current  system  and  consequently  excel  it  in  operation. 

10.  Duplex  Repeaters.  —  Duplex  repeaters  are  not  as 
complicated  in  theory  as  simplex  repeaters,  for  it  is  only 
necessary  to  connect  the  magnet  of  the  pole-changer  that 
controls  one  circuit  with  the  contact  points  of  the  receiving 
relay  of  another  line.  A  still  simpler  arrangement,  dis- 
pensing with  pole-changers,  and  called  a  direct-point  re- 
peater, is  widely  used. 

Polar  Direct-point  Repeater.  —  The  schematic  diagram 
of  the  polar  direct-point  repeater  is  given  in  Fig.  19.  The 
repeating  station  is  equipped  with  four  generators,  D\  and 
A,  two  differentially-wound  polarized  relays,  P\  and  P2, 
and  two  artificial  lines.  The  elements  of  the  originating 
and  receiving  stations  A  and  B  are  also  shown.  When 
both  keys  K  and  K'  are  elevated  they  rest  on  the  rear  con- 


DUPLEX  TELEGRAPHY 


77 


tacts  which  are  connected  to  the  negative  generator  termi- 
nals. For  this  condition  all  four  relay  armatures  will  rest 
against  their  left  contacts,  as  indicated  in  the  figure.  The 
armatures  of  repeater  relays  PI  and  P2  will  be  against  the 
negative  contacts  of  generators  D\  and  Z>2,  no  current  will 
flow  over  either  line  wire,  and  sounders  S  and  S'  will  not 
be  actuated. 

The  depression  of  key  K  causes  a  greater  current  to  flow 
over  the  western  line  and  line  coils  of  relays  P  and  PI 
than  through  their  artificial  line  coils,  and  its  direction 
will  be  such  as  to  move  only  the  armature  of  relay  PI  to 
the  right,  thereby  touching  the  positive  generator  termi- 


Fig.  19. 

nal  .of  DI.  A  greater  current  will  then  flow  over  the 
eastern  line  and  line  coils  of  relays  P2  and  P'  than  through 
their  artificial  line  coils,  and  its  direction  is  such  as  to 
move  only  the  armature  of  relay  P' ',  which  then  closes  the 
local  sounder  circuit.  Thus  key  K  controls  the  operation 
of  repeater  relay  PI,  of  relay  P'  and  of  sounder  5"  at  the 
remote  station.  In  the  same  way  key  K'  controls  the 
operation  of  repeater  relay  P2,  relay  P  and  sounder  S. 

When  both  keys  are  depressed  it  will  be  seen  that  all 
relay  armatures  press  against  their  right-hand  contacts,  no 
current  flows  over  either  line,  and  both  sounders  are  oper- 
ated. Thus  messages  being  transmitted  in  opposite  direc- 


78  TELEGRAPH   ENGINEERING 

tions  over  a  single  wire  are  simultaneously  repeated  without 
interference. 

Fig.  20  shows  the  connections  of  the  direct-point  duplex 
repeater  used  by  the  Postal  Telegraph-Cable  Company. 
The  principle  of  operation  is  identical  with  that  just  de- 
scribed, but  there  are  several  additional  features.  For  the 
operation  of  reading  sounders  Sz  and  S^  at  the  repeating 
station,  the  leak  relays  LI  and  LZ  in  series  with  2o,ooo-ohm 


Fig.  20. 

resistances  r,  r  (shunted  by  i-mf.  condensers)  are  bridged 
from  ground  to  the  armatures  of  the  repeater  relays  PI 
and  PZ-  The  transmission  of  signals  from  one  station  to 
the  other  through  the  repeater  for  the  various  positions  of 
the  keys  can  readily  be  traced,  the  pole-changers  C  and  Cr 
remaining  in  the  positions  shown. 

This  repeater  arrangement  permits  of  separation,  by 
the  upward  movement  of  the  switches  a  and  a',  into  two 
polar-duplex  sets.  Thus  duplex  signalling  may  be  effected 
between  the  left-hand  station  and  the  repeater  station  by 
manipulating  the  key  K\  and  the  distant  key,  and  also 
distinct  duplex  signalling  may  be  carried  on  between  the 


DUPLEX  TELEGRAPHY 


79 


repeater  station  and  the  right-hand  station  by  manipulat- 
ing the  key  K2  and  the  distant  key.  These  sets  differ  from 
those  described  in  connection  with  Figs.  10  and  12  only  in 
the  introduction  of  the  leak  relays.  The  unmarked  coils 
are  3Ooohm  protective  resistances. 

Bridge  Direct- point  Repeater.  —  The  arrangement  of  the 
repeater  used  with  the  bridge  duplex  by  the  Western 
Union  Telegraph  Company  is  shown  in  Fig.  21.  The  in- 
strument positions  represented  are  for  the  normal  con- 
dition, that  is,  no  signals  being  sent  in  either  direction, 
the  positive  generator  terminals  being  connected  to  the 


Fig.  21. 

line  at  both  stations.  Reference  to  the  explanation  of  the 
bridge  duplex  and  Fig.  16  will  indicate  that  the  armatures 
of  the  two  repeater  relays  PI  and  P%  and  Consequently 
those  of  the  leak  relays  LI  and  L%  rest  against  their  left- 
hand  contacts.  Further,  no  current  traverses  the  two 
line  wires,  and  the  two  reading  sounders  63  and  S4  at  the 
repeating  station  are  not  actuated. 

When  the  key  at  the  western  station  is  depressed, 
thereby  bringing  the  line  in  contact  with  the  negative 
terminal  of  the  home  generator,  current  will  flow  through 
the  repeater  relay  PI  from  the  point  x  to  y,  and  conse- 
quently its  armature  will  be  drawn  over  to  the  right. 


80  TELEGRAPH   ENGINEERING 

This  will  cause  the  operation  of  sounder  53  through  the 
leak  relay  LI,  and  the  negative  generator  terminal  will  be 
in  contact  with  the  junction  n  of  the  right-hand  retardation 
coil.  Current  will  then  flow  over  the  eastern  line  and 
through  the  relay  P%  from  the  point  y'  to  x'  so  that  the 
armatures  of  relays  P%  and  Z^  will  remain  as  shown.  The 
eastern  line  current  is  in  such  direction  as  to  operate  the 
polarized  relay  and  sounder  at  the  eastern  station  (see  §  8). 

The  depression  of  both  keys  will  cause  all  armatures  to 
rest  against  their  right-hand  contacts,  thereby  actuating 
the  sounders  Sz  and  ,£4  and  also  the  sounders  at  the  termi- 
nal stations. 

When  the  double-throw  triple-pole  switches  a  and  b  are 
moved  to  the  left,  the  repeater  is  separated  into  two  dis- 
tinct bridge-duplex  sets  that  differ  from  that  already  de- 
scribed only  in  the  addition  of  the  leak  relays.  It  can  be 
seen,  then,  that  the  western  and  repeating  stations  and 
that  the  repeating  and  eastern  stations  can  engage  in 
separate  duplex  signalling,  both  the  repeater  and  leak  re- 
lays being  in  use  in  this  divided  service.  The  resistances 
r  are  adjustable  to  have  the  following  values:  8,000,  12,000, 
16,000  and  20,000  ohms. 

ii.  Half-set  Repeaters.  —  Where  it  is  found  desirable  to 
join  a  duplex  line  with  a  simplex  line  for  through  simplex 
operation  in  either  direction,  a  half-set  repeater  is  used. 
One-half  of  the  apparatus  necessary  for  a  simplex  repeater 
of  any  type  will  serve  as  a  half-set  repeater. 

The  connections  oi  a  Weiny-Phillips  half-set  repeater 
joined  between  a  simplex  line  and  a  polar-duplex  circuit 
are  shown  in  Fig.  22.  The  repeater  apparatus  is  shown 
between  the  two  broken  lines,  while  the  simplex  and 


DUPLEX  TELEGRAPHY 


8l 


duplex  receiving  apparatus  are  shown  respectively  on  the 
left  and  right  sides  as  A  and  B.  This  apparatus  is  usually 
interconnected  at  a  switchboard  by  means  of  flexible 
double-conductor  cords  equipped  with  plugs  or  wedges 
which  fit  into  appropriate  jacks,  these  cords  being  repre- 
sented, for  the  sake  of  simplicity,  by  dotted  lines. 

The  operation  of  the  repeater  transmitter  T  is  con- 
trolled by  the  armature  of  the  polarized  relay  P,  and  the 
operation  of  the  pole-changer  C  is  controlled  by  the  arma- 
ture of  the  repeater  relay  Ri.  The  function  of  the  differ- 


(S) 


Fig.  22. 

ential  holding  coil  H  of  the  Weiny-Phillips  relay  has  been 
explained  in  §  10  of  Chap.  I. 

In  the  normal  condition,  when  the  distant  keys  on  both 
lines  are  depressed  (or  circuit-closers  closed)  current  flows 
over  the  simplex  line,  distant  relay  and  relays  R  and  RI, 
and  the  duplex  line  will  be  in  contact  with  the  negative 
generator  terminal.  The  armature  of  relay  P  will  rest 
against  the  right-hand  contact  regardless  of  the  position  of 
the  armature  of  the  pole-changer  C  (because  the  distant 
pole-changer  makes  contact  with  the  negative  generator 
terminal),  and  consequently  the  armatures  of  sounder  $3 
and  of  transmitter  T  will  be  attracted.  Equal  and  oppos- 


82  TELEGRAPH  ENGINEERING 

ing  currents  traverse  the  windings  of  the  holding  coil  H 
so  that  its  core  is  not  magnetized;  nevertheless  the  arma- 
ture of  the  repeater  relay  will  be  attracted  owing  to  the 
current  in  the  main  coil  RI.  The  attraction  of  this  arma- 
ture closes  the  magnet  circuit  of  pole-changer  C  and  its 
armature  places  the  negative  generator  terminal  in  con- 
tact with  the  junction  m  of  the  relay  windings.  This 
action  does  not  affect  relay  P,  but  the  distant  polarized 
relay  on  the  duplex  line  responds  and  operates  its  local 
sounder. 

When  the  key  at  the  distant  office  on  the  simplex  line 
is  raised,  no  current  flows  through  this  line  and  relays  R  and 
RI,  and,  therefore,  their  armatures  will  be  released.  The 
armature  of  the  repeater  relay  opens  the  circuit  of  the 
pole-changer  magnet  which  causes  the  positive  battery 
terminal  to  be  placed  on  the  junction  m.  The  relay  P 
will  not  be  affected,  but  the  distant  relay  on  the  duplex 
line  will  open  the  home  sounder  circuit.  In  this  way 
signals  formed  by  the  key  on  the  simplex  line  are  repeated 
to  a  distant  station  on  a  duplex  line. 

If,  instead,  the  distant  key  on  the  duplex  line  be  raised, 
the  armature  of  relay  P  will  be  drawn  over  to  the  left- 
hand  side,  causing  the  magnet  of  transmitter  T  to  be  de- 
energized.  This  action  opens  the  simplex  line  at  x,  and 
consequently  the  distant  sounder  on  the  simplex  line  re- 
leases its  armature.  Although  no  current  flows  through 
the  relay  RI  the  magnetism  developed  in  the  core  of  the 
holding  coil  H  by  current  in  one  of  its  coils  is  sufficient  to 
hold  over  the  armature,  which  action  keeps  the  distant 
sounder  on  the  duplex  line  energized.  When  the  key  at 
the  remote  end  of  the  duplex  line  is  again  depressed,  the 
armature  of  relay  P  is  drawn  to  the  sounder  contact  and 


DUPLEX  TELEGRAPHY  83 

the  armature  of  the  transmitter  is  again  attracted,  thereby 
closing  the  simplex  line  at  the  repeating  station.  Thus 
the  composite  circuit  operates  as  a  closed-circuit  simplex 
line. 

Some  important  duplex  circuits  are  operated  simplex 
through  half-set  repeaters  by  current  reversals  instead  of 
ordinary  Morse  simplex  operation,  because  of  higher  speed 
possibilities  and  lesser  dependence  upon  weather  con- 
ditions. The  Associated  Press  leased  wire  is  operated  in 
this  way,  the  signalling  being  carried  out  by  mecograph 
transmitters. 

PROBLEMS. 

1.  A  perfectly-insulated  differential  duplex  line  has  a  resistance  of 
1500  ohms  and  is  equipped  with  a  i4o-ohm  differential  relay  at 
each  end.    If  the  battery  resistance  is  200  ohms,  calculate  the  proper 
resistance  of  the  artificial  lines. 

2.  When  one  key  of  the  circuit  of  Prob.  i  is  closed,  thereby  in- 
troducing a  1 60- volt  battery,  how  much  current  flows  through  the 
line  and  through  each  artificial  line  ? 

3.  A  2000-ohm  polar-duplex  line  has  a  3oo-ohm  polarized  relay, 
and  a   2644-ohm  artificial  line  at  each  end.     Using  6oo-ohm  re- 
sistances in  series  with  the  2oo-volt  generators,  determine  the  current 
strength  in  each  relay  coil  for  the  various  positions  of  the  signalling 
keys. 

4.  If  the  line  of  the  preceding  problem  be  operated  on  380  volts 
as  a  leak  duplex  with  22oo-ohm  leak  paths,  compute  the  current 
strengths  in  the  relay  coils  when  one  key  is  depressed  and  when  both 
keys  are  either  raised  or  depressed. 

5.  A  Morris  duplex  line,  having  800  ohms  resistance,  employs  a 
3oo-ohm  polarized  relay  at  one  end  and  a  i4o-ohm  differential  neutral 
relay  at  the  other  end.     Using  6oo-ohm  protective  resistances  in 
series  with  the  generators,  determine  the  proper  resistance  values  of 
the  artificial  line  and  compensating  rheostat. 

6.  Derive  equation  (9)  for  the  terminal  resistance  of  a  bridge- 
duplex  circuit. 


84  TELEGRAPH  ENGINEERING 

7.  What  should  be  the  resistance  of  the  artificial  lines  used  with 
a  perfectly-insulated  bridge-duplex  circuit  having  a  looo-ohm  line, 
when  using  6oo-ohm  polarized  relays,  2oo-ohm  protective  resistances 
and  5oo-ohm  (each  winding)  retardation  coils? 

8.  If  in  unfavorable  weather  conditions  the  line  of  Probs.  i  and  2 
has  a  total  leakage  resistance  to  ground  of  1500  ohms,  considered 
concentrated  at  the  mid-point  of  the  line,  determine  the  relay  ad- 
justment that  will  cause  satisfactory  operation. 


CHAPTER   III 

QUADRUPLEX  TELEGRAPHY 

i.  Quadruplex  Systems.  —  A  quadruplex  telegraph  sys- 
tem provides  for  the  simultaneous  transmission  of  two 
groups  of  signals  in  one  direction  and  also  two  groups  of 
signals  in  the  opposite  direction  without  interference  over 
a  single  telegraph  line.  When  in  full  use,  eight  operators 
are  required  for  each  quadruplex  circuit,  two  receiving 
and  two  sending  operators  being  located  at  each  terminal 
station.  Quadruplex  signalling  was  devised  by  Thomas 
A.  Edison,  and  was  first  placed  in  operation  in  1874  by  the 
Western  Union  Telegraph  Company.  It  is  now  employed 
on  many  lines  over  distances  up  to  500  miles. 

Quadruplex  systems  are  generally  based  on  a  combi- 
nation at  each  station  of  the  single-current  and  double- 
current  duplex  systems,  which  have  been  described  in  the 
foregoing  chapter.  The  single-current,  or  Stearns  duplex, 
permits  of  the  simultaneous  transmission  of  one  message 
in  each  direction  through  changes  in  current  intensity,  and 
the  double-current  system,  either  the  polar  or  bridge 
duplex,  permits  of  the  simultaneous  transmission  of  one 
message  in  each  direction  through  changes  in  current 
direction.  When  these  duplex  systems  are  combined  to 
form  a  quadruplex  circuit,  the  latter  is  called  the  polar 
side,  or  first  side,  of  the  system,  and  the  former  is  called  the 
neutral  side,  or  second  side,  of  the  system. 

The  manner  in  which  these  systems  are  combined  is 

85 


86  TELEGRAPH   ENGINEERING 

illustrated  in  Fig.  i,  which  shows  one  station  A  equipped 
with  apparatus  only  for  sending  and  the  other  station  B 
equipped  with  apparatus  only  for  receiving  messages. 
This  circuit  permits  of  the  simultaneous  transmission  of 
two  independent  messages  over  one  wire  in  the  same 
direction,  which  transmission  is  called  diplex  signalling. 
Key  K  is  a  form  of  continuity-preserving  pole-changer, 
which,  when  depressed,  causes  its  lever  contact  a  to  raise 
the  upper  spring  u  away  from  the  fixed  contact  b,  and  per- 
mits the  lower  spring  /  to  follow  until  it  strikes  against  this 
fixed  contact.  The  key  Kf  is  a  transmitter  which  changes 
the  number  of  cells  of  the  battery  B  which  is  included  in 


Fig.  i. 

the  circuit.  Both  keys  are  normally  held  in  their  upper 
positions  by  retractile  springs.  Relay  R  is  a  neutral  relay 
which  has  its  spring  so  adjusted  that  the  armature  will  not 
be  attracted  when  the  small  current,  supplied  by  the  left- 
hand  part,  or  short  end,  of  the  battery  traverses  the  relay 
winding,  but  will  be  attracted  when  supplied  with  current 
from  the  entire,  or  long  end,  of  the  battery.  Instantaneous 
reversal  of  current  direction  has  no  effect  upon  this  relay 
(see  §  3).  The  polarized  relay  P  responds  only  to  cur- 
rent reversals  and  is  not  influenced  by  changes  in  current 
intensity,  so  long  as  this  intensity  exceeds  3  to  5  milli- 
amperes. 
When  neither  key  is  depressed  the  short  end  of  the 


QUADRUPLEX  TELEGRAPHY  87 

battery  is  in  circuit  and  key  contacts  a  and  b  are  re- 
spectively connected  to  the  negative  and  positive  battery 
terminals.  It  will  be  seen  that  the  current  then  flowing  is 
not  strong  enough  to  operate  the  neutral  relay  R  and  is 
in  the  wrong  direction  to  operate  the  polarized  relay  P. 
When  key  K  is  depressed  (as  shown  in  the  figure)  the  cur- 
rent flowing  is  not  altered  in  intensity,  but  is  reversed  in 
direction,  and  consequently  relay  P  responds  and  causes 
the  actuation  of  its  sounder  6*2  through  the  local  battery 
Bf.  When  key  K'  is  also  depressed  the  direction  of  current 
flow  remains  unaltered  but  its  intensity  is  now  sufficient  to 
operate  neutral  relay  R,  which  in  turn  operates  sounder  Si. 
Thus,  pole-changing  key  K  controls  the  polarized  relay, 
and  the  transmitting  key  K'  independently  controls  the 
neutral  relay,  thereby  enabling  the  simultaneous  trans- 
mission of  two  messages  from  one  station  to  another  over 
a  single  wire. 

2.  Operation  of  Quadruplex  Systems.  —  By  duplicating 
the  apparatus  necessary  for  the  diplex  circuit  just  de- 
scribed and  employing  differentially-wound  relays  and  an 
artificial  line  at  each  end  of  the  line  wire,  as  in  the  duplex 
systems,  it  is  possible  to  send  two  messages  in  each  direc- 
tion at  the  same  time,  thereby  affording  quadruplex  tele- 
graphic signalling.  Such  a  quadruplex  circuit  extending 
between  two  stations  A  and  B,  and  operated  by  batteries, 
is  shown  in  Fig.  2.  It  will  be  observed  that  the  pole- 
changers  C  and  C'  are  electromagnetically  controlled  by  the 
keys  K  and  K'j  and  that  the  transmitters  T  and  T  are 
similarly  controlled  by  the  keys  K\  and  Kz.  The  short 
ends  of  the  main  batteries  B  and  Bf  are  connected  in  circuit 
when  the  keys  KI  and  K2  are  open,  and  the  entire  batteries 


88 


TELEGRAPH   ENGINEERING 


are  in  circuit  when  these  keys  are  depressed.  The  figure 
shows  the  long-end  battery  to  have  three  times  as  many  cells 
as  the  short-end  battery.  The  positive  and  negative  ter- 
minals of  these  batteries  are  connected  to  the  line  junctions 
x,  y,  when  the  keys  K  and  K'  are  raised  and  depressed 
respectively. 

The  figure  represents  the  condition  when  the  circuit  is  idle, 
all  four  keys  being  in  the  raised  position.  In  this  condition 
the  positive  terminals  of  the  short  ends  of  both  main-line 
batteries  are  joined  to  the  junctions  x  and  y,  consequently  no 
current  flows  through  the  line  coils  of  all  relays  nor  through 
the  line  wire.  A  current  will  flow,  however,  from  each 


Fig.  2. 

main  battery  through  the  artificial  line  coils  of  both  re- 
lays, through  the  artificial  line,  and  back  to  the  other 
battery  terminal.  These  currents  are  too  weak  to  oper- 
ate the  neutral  relays  R  and  R',  and  they  are  in  the  wrong 
direction  to  operate  the  polarized  relays  P  and  P'.  Con- 
sequently the  armatures  of  all  sounders,  S,  S',  Si  and  62, 
will  remain  drawn  up  by  their  retractile  springs. 

When  key  K  is  depressed  the  armatures  of  pole-changer 
C  will  be  attracted  and  the  negative  terminal  of  the  home 


QUADRUPLEX  TELEGRAPHY  89 

battery  will  be  connected  to  the  junction  x,  and  the  posi- 
tive terminal  will  be  grounded.  The  main-line  batteries 
are  now  cumulatively  connected,  and  more  current  traverses 
the  line  and  line  coils  of  all  relays  than  flows  through  the 
artificial  lines  and  artificial  line  coils  of  these  relays.  For 
ease  in  presentation,  let  the  current  traversing  the  artificial 
lines  be  considered  of  unit  intensity,  and  let  the  adjust- 
ment of  these  lines  be  such  that  the  current  in  the  line 
wire  when  either  key  K  or  K'  only  is  depressed  be  2 
units.  Currents,  then,  of  i  unit  intensity  flow  through 
the  artificial  line  coils  of  all  relays,  and  opposing  currents 
of  2  units  intensity  flow  through  their  line  coils.  The 
surplus  of  i  unit  current  through  all  the  line  coils  of  the 
relays  is  insufficient  to  actuate  the  neutral  relays  R  and 
R'\  it  is  in  the  proper  direction  to  operate  polarized  relay 
P',  but  is  in  the  wrong  direction  to  operate  polarized  re- 
lay P.  In  the  same  way,  the  depression  of  key  Kf  only 
causes  the  operation  of  relay  P.  Thus  the  depression  of 
a  pole-changing  key  causes  the  operation  of  the  distant 
polarized  relay  and  the  actuation  of  the  sounder  con- 
trolled by  it. 

The  depression  of  both  pole-changing  keys  places  the  nega- 
tive battery  terminals  to  the  junctions  x  and  y,  and,  since 
the  two  identical  main-line  batteries  are  opposed  to  each 
other,  no  current  flows  over  the  line  wire.  Currents  of 
unit  intensity  flow  through  the  artificial  line  coils  of  all 
relays,  and,  as  before,  are  too  weak  to  operate  the  neutral 
relays  R  and  R' .  The  direction  of  these  currents  is  such 
as  to  operate  both  polarized  relays. 

The  closing  of  key  KI,  all  other  keys  being  open,  intro- 
duces the  long  end  of  battery  B  into  the  circuit.  Its 
voltage  being  assumed  three  times  that  of  the  short-end 


90  TELEGRAPH  ENGINEERING 

battery  B',  the  opposing  line  currents  will  not  neutralize, 
but  a  current  of  2  units  will  flow  from  station  A  to  sta- 
tion B  and  through  the  line  coils  of  all  relays.  At  station 
A  a  current  of  3  units  intensity  flows  through  the  arti- 
ficial line  coils  of  the  relays  and  artificial  line,  while  at 
the  other  station  a  current  of  i  unit  intensity  flows  through 
the  corresponding  circuit.  The  currents  through  the  two 
coils  of  relay  R  are  in  opposite  directions  around  the  core 
and,  consequently,  partially  neutralize  each  other,  the 
surplus  of  i  unit  current  being  insufficient  to  operate  this 
instrument.  This  surplus  current  in  the  artificial  line  coils 
of  the  relay  P  is  in  such  direction  as  to  hold  its  armature 
away  from  the  sounder  contact.  The  currents  through 
the  two  coils  of  relay  Rf  are  in  the  same  direction  around 
the  core  and  are  equivalent  to  a  current  of  3  units  travers- 
ing a  single  coil.  This  current  is  strong  enough  to  operate 
relay  R'}  for  this  instrument  is  so  adjusted.  The  currents 
flowing  through  the  coils  of  polarized  relay  P'  are  both 
in  the  wrong  direction  to  operate  this  instrument.  Thus, 
the  depression  of  key  K\  causes  the  operation  of  neutral 
relay  R'\  similarly  the  closing  of  key  KZ  causes  the  opera- 
tion of  neutral  relay  R. 

The  depression  of  both  keys  KI  and  K2  connects  the  long 
ends  of  both  batteries  to  the  circuit.  No  current  flows 
over  the  line  wire,  but  currents  of  3  units  intensity  traverse 
the  artificial  line  coils  of  all  relays.  These  currents  are 
sufficiently  strong  to  operate  the  neutral  relays  R  and  R' ', 
but  are  in  the  wrong  direction  to  operate  the  polarized  re- 
lays P  and  P' .  Sounders  S  and  5",  therefore,  respond  to 
the  depression  of  both  transmitting  keys  KI  and  Kz. 

When  keys  K  and  KI  are  closed,  the  negative  terminal  of 
the  long-end  battery  B  is  joined  to  the  point  x,  while  the 


QUADRUPLEX  TELEGRAPHY  91 

positive  terminal  of  the  short-end  battery  Bf  is  joined  to 
the  point  y.  A  current  of  4  units  intensity  will  flow  over 
the  line  from  the  right  toward  the  left,  a  current  of 
3  units  will  flow  through  the  artificial  line  circuit  at  the 
left  and  a  current  of  i  unit  will  flow  through  the  artificial 
line  circuit  at  the  right.  It  will  be  seen  that  the  relays 
P'  and  Rf  respond,  thereby  operating  sounders  S2  and  S'. 

In  the  same  manner,  the  currents  in  the  various  portions 
of  the  circuit  and  the  relays  affected,  for  the  remainder  of  the 
16  possible  combinations  of  key  positions,  may  be  traced. 
Having  given  the  constants  of  any  circuit,  the  currents 


r3<0oo 


Fig.  3. 

traversing  the  various  relay  coils  can  be  determined  in  the 
usual  manner. 

The  main-circuit  connections  of  one  station  of  a  quad- 
ruplex  circuit,  using  the  Field  key  system  with  a  single 
generator  instead  of  the  battery,  are  shown  in  Fig.  3.  The 
function  of  the  pole-changer  C  is  the  reversal  of  the  gen- 
erator Dj  while  that  of  the  transmitter  T  is  the  variation 
of  available  potential  difference  by  means  of  the  resist- 
ances r-i  and  r3.  When  the  armature  of  the  transmitter  is 


92  TELEGRAPH  ENGINEERING 

attracted,  the  added  resistance  r2  is  short-circuited  and  the 
resistance  from  the  point  x  to  ground  at  G  is  2  X  300  or 
600  ohms,  and  when  this  armature  is  released  the  resist- 

.     ooo  (1200  +  600)  ,    , 

ance  is  —  —  ^  or  600  ohms,  as  before.     The 

900  +  1  200  +  600 

terminal  resistance  therefore  remains  unaltered  regardless 
of  the  position  of  the  transmitter  armature. 

To  consider  the  variation  in  current  produced  by  the 
movements  of  the  transmitter  armatures,  let,  as  in  the 
preceding  chapter: 

Rp  =  resistance  of  polarized  relays, 

Rr  =  resistance  of  neutral  relays, 

Rb  =  resistance  of  protective  coils  in  series  with 

generators, 

r  =  resistance  of  artificial  lines, 
and      E  =  voltage  of  generator. 

Then,  if  the  apparatus  at  the  distant  station  is  also  as 
shown  in  Fig.  3  (that  is,  all  keys  open),  the  line  current  is 
zero  and  the  current  supplied  by  each  generator  is 

7  =  _  E  _  ,  . 

' 


„ 


of  which,  the  part  that  traverses  the  artificial  line  circuit  is 

E-I(Rb  +  ra)  . 


the  remainder  traversing  the  leak  resistance  r3.  When  the 
armatures  of  both  transmitters  are  attracted,  the  current 
flowing  through  the  artificial  line  circuit  is 


QUADRUPLEX  TELEGRAPHY  93 

Thus,  if  the  resistances  of  the  various  paths  are  as  indi- 
cated in  the  figure,  the  currents  traversing  the  artificial 
line  circuit  when  the  transmitter  armatures  are  both  re- 
leased and  when  both  attracted  are  respectively  35.3  and 
106  milliamperes.  The  attraction  of  the  armatures  thus 
triples  the  current  flowing  and  this  larger  current  is  sufficient 
to  operate  the  neutral  relays.  The  currents  for  other  key 
positions  might  be  similarly  determined. 

At  times  it  is  feasible  to  raise  the  current  ratio  from  3  to 
i  up  to  4  to  i,  which  may  be  done  by  changing  the  added 
resistance  to  1800  ohms  and  altering  the  leak  resistance  to 
800  ohms,  if  the  resistance  in  series  with  the  generator 
remains  the  same.  For  any  other  current  ratio  r,  or 
other  series  generator  resistance  Rb,  the  added  and  leak 
resistances  should  be  respectively 

rz  =  Rb(r-  i)  (4) 

and 

.  ,-.  (5) 


^ 

In  practice  two  generators  at  each  station  are  more  fre- 
quently employed  in  quadruplex  service  than  one  gener- 
ator. The  connections  of  one  station,  according  to  the 
Field  key  system  with  two  generators,  are  shown  in  Fig.  4. 
Its  similarity  to  the  preceding  figure  will  be  noticed,  and 
consequently  the  foregoing  equations  apply  to  this  ar- 
rangement also.  The  relay  contacts  marked  S  are  those 
against  which  the  armatures  must  rest  in  order  to  operate 
the  sounders. 

To  balance  a  quadruplex  circuit  the  distant  generators 
may  be  disconnected  from  the  circuit  while  the  resistance 
of  the  home  artificial  line  is  adjusted  to  equal  the  resist- 
ance of  the  line  plus  the  terminal  apparatus  at  the  other 


94 


TELEGRAPH  ENGINEERING 


end.     In  order  that  the  removal  of  the  distant  generators 
will  not  alter  the  terminal  resistance,  a  switch,  Si,  is  ar- 


Fig.4- 

ranged  to  introduce  a  resistance  rg  from  the  junction  x  to 
ground  which  equals  the  resistance  connected  in  series 
with  the  generators. 

3.  Avoidance  of  Sounder-armature  Release  During 
Current  Reversals  in  Neutral  Relay.  —  When  a  neutral  re- 
lay of  a  quadruplex  circuit  is  actuated,  and  the  position  of 
the  pole-changing  key  at  the  other  station  is  altered  mean- 
while, the  magnetism  in  the  core  of  this  relay  is  reversed. 
This  means  that  the  magnetism  falls  to  zero  and  then 
rises  to  the  same  intensity  in  the  opposite  direction.  As  a 
consequence  the  attracting  force  also  passes  through  zero, 
and  a  moment  exists  when  the  relay  armature  is  not  held 
against  its  front  contact  point.  During  this  brief  interval 
the  local  sounder  circuit  is  opened  and  the  sounder  armature 
is  momentarily  released.  In  the  operation  of  a  quadruplex 
system  such  periods  of  zero  magnetism  in  the  neutral 
relay  cores  are  constantly  recurring,  and  result  in  false 
signals. 


QUADRUPLEX  TELEGRAPHY 


95 


Fig.  5. 


Various  methods  have  been  adopted  for  avoiding  the 
release  of  the  sounder  armature  during  these  short  non- 
magnetization  periods  of  the  neutral  relay.  One  method 
has  already  been  mentioned  in  connection  with  the  Morris 
duplex  system,  described  in  §  7  of  the  fore- 
going chapter;  namely,  the  insertion  of  a 
repeating  sounder.  The  connections  of  the 
local-sounder  and  repeating-sounder  cir- 
cuits are  illustrated  in  Fig.  5.  The  repeat- 
ing sounder  RS  has  a  heavy  armature  lever 
so  as  to  render  its  action  slow.  It  is  evi- 
dent that  when  the  magnetism  of  the  neu- 
tral relay  R  passes  through  its  zero  value, 
the  relay  armature  would  have  to  be  drawn  against  its 
rear  contact  before  the  sounder  S  would  release  its  arma- 
ture. Since,  in  practice,  the  relay  armature  falls  back  but 
a  small  distance  before  magnetism  of  sufficient  intensity 
in  the  opposite  direction  is  again  established  to  attract  the 
armature,  it  follows  that  no  false  signals  will  arise. 

Another  device,  for  accomplishing 
this  result,  now  extensively  used  on 
the  quadruplex  circuits  of  the  Postal 
^  Telegraph- Cable  Company,  is  the  Diehl 
relay  arrangement,  which  is  shown  in 
Fig.  6.  It  will  be  observed  that  the 
sounder  5*  is  actuated  as  long  as  the 
armature  of  relay  R  is  away  from  its 
rear  stop.  When  this  armature  touches 
its  rear  contact,  the  local  battery,  which  supplies  current 
to  the  relay  R',  is  short-circuited  through  a  protective  re- 
sistance, and  consequently  neither  this  relay  nor  the 
sounder  is  energized. 


Fig.  6. 


96 


TELEGRAPH  ENGINEERING 


Neutral  relays  equipped  with  an  extra  coil,  which  re- 
ceives current  during  the  period  of  current  reversal  in  the 
other  coils  from  a  condenser  or  from  a  reactor,  are  also 
used  in  order  to  avoid  false  signals.  The  arrangement 
used  by  the  Western  Union  Telegraph  Company  with  its 
quadruplex  circuits  is  shown  in  Fig.  7.  Each  winding  of 

the  main  relay  has  a  resistance 
of  350  ohms  while  the  extra  or 
holding  coil  H  has  a  resistance 
of  225  ohms.  The  condenser 
C  has  a  capacity  of  about  3 
microfarads.  As  the  condenser 
is  charged  to  the  difference  of 
potential  across  the  points  a 
and  b,  the  instant  the  dis- 
tant pole-changer  armature  leaves  either  contact  in  the 
act  of  reversing  the  polarity  of  the  distant  generator, 
the  condenser  immediately  discharges  through  the  hold- 
ing coil,  thus  keeping  the  armature  attracted  during 
the  interval  that  the  current  reverses  in  the  main  relay 
coils.  The  Freir  self -polarizing  neutral  relay  also  gives 
satisfaction  with  quadruplex  systems. 

In  order  that  the  period  of  current  reversal  be  as  short 
as  possible  the  movements  of  the  pole-changer  armatures 
between  their  contacts  should  be  reduced  as  much  as  prac- 
ticable. Quick  reversals  of  magnetism  in  the  relay  cores 
are  made  possible  by  the  use  of  relays  possessing  little 
inductance  and  having  laminated  cores. 

4.  The  Postal  Quadruplex.  —  The  Davis-Eaves  quad- 
ruplex is  now  largely  used  by  the  Postal  Telegraph-Cable 
Company,  and  is  illustrated  in  Fig.  8,  which  shows  the  ap- 


QUADRUPLEX  TELEGRAPHY 


97 


paratus  at  one  station.  This  arrangement  is  modelled 
after  the  improved  polar  duplex  described  in  §  6  of  the  fore- 
going chapter.  The  functions  of  the  bridge  coils  g  and  h 
with  the  bridged  condenser  c,  and  the  shunt  paths  con- 
taining the  resistances  /  and  /'  and  the  condensers  Ci  and 
cij  have  there  been  explained.  The  operation  of  the 
transmitter  T  in  varying  the  available  potential  by  means 
of  the  leak  resistance  r3  and  the  added  resistance  rz  has 
been  considered  in  connection  with  Figs.  3  and  4.  The 
condenser  c3  curbs  the  sparking  at  the  transmitter  contacts. 
The  pole-changer  C  and  the  transmitter  T  are  equipped 
with  permanent  magnets,  />/>,  so  arranged  as  to  hasten  the 


return  of  their  armatures  to  the  rear  contact  points. 
Neutral  relay  R  controls  the  operation  of  sounder  Si 
through  the  Diehl  relay  R' ',  as  explained  by  means  of 
Fig.  6.  A  high-resistance  leak  path  to  ground  is  provided 
by  closing  a  switch  introducing  resistance  r' .  Four  local 
generators  are  shown  in  order  to  avoid  complication  of 
the  diagram,  but  in  practice  only  one  generator  is  em- 
ployed. The  constants  of  the  main  circuit  are:  resistances 
of  g  =  h  =  500  ohms,  of  /  =  /'  =  r^  =  600  ohms,  of  r$  =  450 
ohms,  of  R  —  60  ohms,  of  P  =  200  ohms,  and  of  r'  —  25,000 
ohms;  capacities  of  c\  =  c\  =  c$  =  i  microfarad,  and  of 


98 


TELEGRAPH  ENGINEERING 


c  =  1 2  microfarads.    The  generator  voltage  should  be  from 
250  to  385  volts. 

5.  The  Western  Union  Quadruplex.  —  The  quadruplex 
circuits,  now  the  standard  of  the  Western  Union  Telegraph 
Company,  embody  the  principles  of  the  bridge  duplex, 
already  considered  in  §  8  of  Chap.  II.  The  connections  of 
the  apparatus  at  one  station  of  the  Western  Union  quad- 
ruplex are  shown  in  Fig.  9.  The  retardation  coil  7, 
the  milliammeter  A,  the  pole-changer  C,  the  line  resist- 
ance box,  and  the  method  of  quenching  the  sparking  at 
the  pole-changer  contacts  have  already  been  described 
in  connection  with  the  bridge  duplex.  The  variation  in 


Fig.  9. 

available  potential  is  again  effected  by  the  Field  system,  T 
being  the  transmitter  and  rz  and  r$  being  respectively  the 
added  and  leak  resistances.  Both  the  repeating  sounder 
and  neutral-relay  holding-coil  methods  (see  §  3)  are  utilized 
in  tiding  over  the  period  of  zero  magnetization  in  the 
neutral  relay  core.  Each  artificial  line  is  adjusted  to 
equal,  in  resistance  and  capacity,  the  main-line  wire  plus 
the  apparatus  at  the  distant  station.  The  ground  resist- 
ance rg  facilitates  line  balancing.  This  resistance  is  also 
contained  in  the  artificial  line  box,  as  shown  in  Fig.  6  of 
the  preceding  chapter,  and  connects  with  the  terminal 
marked  "Ground  Balance." 


QUADRUPLEX  TELEGRAPHY  99 

When  the  distant  pole-changer  places  the  negative  gen- 
erator terminal  to  the  line,  the  armature  of  the  polarized 
relay  at  the  home  station  will  close  its  local  sounder  circuit, 
but  when  it  places  the  positive  terminal  to  the  line  the 
polarized  relay  will  not  operate  its  sounder.  An  alteration 
in  current  intensity  from  a  minimum  to  a  maximum  value, 
or  vice  versa,  does  not  affect  the  polarized  relay  whether 
it  be  against  one  contact  or  the  other.  Each  polarized  re- 
lay is  unaffected  by  the  movements  of  the  home  pole- 
changer. 

The  neutral  relay  is  connected  in  the  circuit  exactly  as 
in  Fig.  2,  that  is,  one  winding  is  connected  in  series  with 
the  line  wire  while  the  other  is  connected  in  series  with  the 
artificial  line.  Each  neutral  relay  operates  only  on  the 
attraction  of  the  armature  of  the  distant  transmitter,  for 
the  current  then  traversing  this  receiving  instrument  is 
three  times  as  great  as  when  the  transmitter  armature  is 
not  attracted,  and  because  the  retractile  spring  on  the  re- 
lay is  adjusted  so  that  its  armature  will  not  be  attracted 
when  the  relay  is  traversed  by  the  weaker  current. 

The  charge  residing  in  the  condenser  c,  bridged  across 
the  line  and  artificial  line  through  the  holding  coil  of  the 
neutral  relay,  will  be  relieved  whenever  the  distant  pole- 
changer  armature  leaves  either  contact.  This  discharge 
causes  a  pulse  of  current  to  traverse  the  holding  coil, 
which  pulse  is  sufficient  to  hold  the  armature  of  the  neutral 
relay  (if  attracted  prior  to  current  reversal),  against  the 
front  contact  while  the  reversal  of  magnetism  takes  place 
in  the  main  cores  of  the  relay.  As  a  further  safeguard 
against  the  development  of  false  incoming  signals  on  the 
second  side  of  the  quadruplex  the  repeating  sounder  RS 
is  used. 


100 


TELEGRAPH   ENGINEERING 


The  constants  of  the  main  circuit  are:  resistances  of 
coils  a  =  b  =  500  ohms,  of  resistance  lamps  in  each  main 
potential  lead  =  600  ohms,  of  r?  =  1200  ohms,  of  r$  = 
900  ohms,  P  =  600  or  800  ohms,  R  =  700  ohms  and 
rg  =  600  ohms;  capacities  of  c'  =  i  microfarad,  and  of 
c  =  i  to  3  microfarads.  The  generator  voltage  should  be 
sufficient  to  develop  a  current  of  from  0.09  to  0.15  am- 
pere in  the  line  wire  when  both  transmitters  and  one  pole- 
changer  are  closed. 

When  extremely  bad  weather  renders  the  second  side  of 
the  quadruplex  inoperative,  the  quadruplex  circuit  may 
be  used  as  a  duplex  circuit  by  keeping  the  two  trans- 
mitters closed. 

6.  Quadruplex  Repeaters.  —  In  general,  any  two  quad- 
ruplex sets  can  be  connected  together  to  form  a  quadruplex 
repeater.  The  scheme  of  connections  of  a  quadruplex 


•WEST 
LINE 


Fig.    10. 

repeater  is  shown  in  Fig.  10.  The  polarized  relays  PI  and 
Pz  control  the  operation  of  pole-changers  C\  and  Cz  re- 
spectively, and  the  neutral  relays  RI  and  R2  control  the 
operation  of  transmitters  T"2  and  T\  respectively.  It  is 
possible  also  to  have  the  pole-changers  controlled  by  the 


QUADRUPLEX  TELEGRAPHY  ibl 

neutral  relays  and  the  transmitters  by  the  polarized  re- 
lays. For  more  satisfactory  operation  repeating  sounders 
may  be  interposed  between  each  neutral  relay  and  its 
corresponding  transmitter,  as  already  explained. 

The  armature  positions  indicated  in  the  figure  are  for 
the  normal  condition,  that  is,  when  all  keys  at  both  eastern 
and  western  stations  are  open.  This  means  that  the 
positive  terminal  of  the  short-end  battery  or  generator  is 
joined  to  the  line  at  each  station  as  well  as  at  the  repeat- 
ing station.  The  generators  at  the  repeating  station  are 
not  shown,  but  the  pole-changer  contacts  are  marked  to 
show  their  respective  polarities  (the  other  generator  termi- 
nals are  grounded). 

When  the  pole-changing  key  at  the  western  station 
is  depressed,  twice  as  much  current  flows  (toward  the 
western  station)  through  the  line  coils  of  relays  Ri  and  PI 
as  through  their  other  coils.  This  causes  the  operation  of 
relay  PI  but  not  of  relay  Rlm  The  armature  of  pole-changer 
Ci  is  attracted,  thereby  placing  the  negative  generator 
terminal  to  the  eastern  line.  This  action  does  not  affect 
the  repeater  relays  R2  and  P2  nor  the  distant  neutral  re- 
lay, but  only  the  eastern  polarized  relay. 

If,  instead,  the  transmitter  key  at  the  western  station 
be  depressed,  the  long  end  of  the  home  battery  or  gener- 
ator will  be  joined  to  the  line.  Twice  as  much  current 
flows  (toward  the  repeating  station)  through  the  line  coils 
of  relays  RI  and  PI  as  through  their  artificial  line  coils. 
This  causes  the  operation  of  relay  RI  but  not  of  relay  PI. 
The  attraction  of  the  relay  armature  energizes  the  trans- 
mitter T2,  which  impresses  the  greater  generator  voltage  at 
the  repeating  station  on  the  eastern  line.  This  causes 
more  current  to  flow  through  the  artificial  line  coils  of 


102  TELEGRAPH  ENGINEERING 


relays  R2  and  P2  than  through  their  other  coils.  The 
surplus  current  is  insufficient  to  operate  relay  R%  and  in 
the  wrong  direction  to  operate  relay  P2-  The  distant  neu- 
tral relay  only  responds  to  the  depression  of  the  western 
transmitter  key. 

In  the  same  way  the  conditions  may  be  traced,  for 
other  key  positions  at  the  two  terminal  stations,  through 
the  repeating  station. 

It  is  practicable  to  secure  quadruplex  operation  over  a 
portion  of  a  line  that  at  other  portions  is  operated  duplex. 
Thus,  a  number  of  lines  between  New  York  and  Chicago 
are  operated  polar  duplex  between  these  terminal  sta- 
tions, and  are  also  simultaneously  operated  differential 
duplex  between  New  York  and  Buffalo.  Such  a  circuit 
requires  repeating  apparatus  at  Buffalo  that  is  formed  by 
combining  a  direct-point  duplex  repeater  with  a  quadru- 
plex set. 

7.  Duplex-diplex  Signalling.  —  A  system  of  telegraphy 
that  permits  of  duplex  or  diplex  transmission,  but  not 
both  simultaneously  as  in  quadruplex  signalling,  is  called 


ll|c 


Fig.  ii. 


a  duplex-diplex  system.  One  such  system,  devised  by 
Crehore,  utilizes  both  an  alternating  current  and  a  direct 
current,  these  currents  being  separated  by  means  of  in- 
ductances and  condensers.  Fig.  n  shows  the  schematic 


QUADRUPLEX  TELEGRAPHY          103 

arrangement  of  apparatus  at  one  station  for  an  open- 
circuit  duplex-diplex  system. 

Continuity-preserving  keys  KI  and  K2  respectively  con- 
trol the  currents  supplied  by  the  battery  B  and  alternator 
A.  The  neutral  relay  R  and  the  polarized  relay  P  are  in 
parallel  with  each  other,  and  in  series  with  the  line.  The 
inductance  of  the  polarized  relay  is  neutralized  by  the 
properly-adjusted  condenser  C.  The  key  K2  is  shunted  by 
a  reactor  /  which  has  large  inductance  but  little  resistance. 

If  key  KI  is  depressed,  a  direct  current  flows  through 
relay  R  and  no  current  flows  through  relay  P  because  of 
the  presence  of  condenser  C.  Thus  relay  R  as  well  as  the 
distant  neutral  relay  will  operate  on  the  depression  of  the 
direct-current  key  KI. 

Depression  of  key  K%  introduces  the  alternator  into  the 
circuit,  as  shown.  Because  of  the  high  inductance  of  re- 
lay R,  only  a  small  current  will  flow  through  it,  and  its 
retractile  spring  is  adjusted  so  that  the  armature  will  not 
be  attracted  on  this  weak  current.  Polarized  relay  P  as  well 
as  the  distant  polarized  relay  will,  however,  be  actuated. 

In  this  way  either  duplex  or  diplex  transmission  may  be 
effected,  the  corresponding  home  instruments  being  also 
responsive  to  the  outgoing  signals.  In  duplex  signalling 
one  direct-current  key  and  one  alternating-current  key 
must  be  used.  Alternating  currents  of  fifty  to  one  hun- 
dred and  fifty  cycles  may  advantageously  be  employed. 
A  quadruplex  system  may  also  be  built  up  on  the  fore- 
going principles  by  applying  alternating  current  to  the 
ordinary  duplex  systems. 

8.  Phantoplex  System.  —  To  increase  the  message- 
carrying  capacity  of  simplex,  duplex  or  quadruplex  lines  by 


104 


TELEGRAPH  ENGINEERING 


additional  superimposed  channels,  the  so-called  phanto- 
plex  system  is  employed  by  the  Postal  Telegraph-Cable 
Company.  The  arrangement  of  this  system  adapted  to  a 
quadruplex  circuit  and  thereby  affording  sextuplex  signal- 
ling, that  is,  the  transmission  of  three  messages  in  each 
direction  simultaneously  without  interference,  is  shown  in 
Fig.  12  for  one  station.  The  quadruplex  connections  will 
be  recognized  as  those  of  the  Field  key  system  and  ex- 
plained with  the  aid  of  Fig.  4,  the  local  circuits  being 
omitted  for  simplicity. 


Fig.  12. 

The  secondary  winding  of  a  sending  transformer,  /,  is 
introduced  between  the  armature  of 'the  transmitter  and 
the  junction  of.  the  neutral  relay  windings.  The  primary 
winding  of  this  transformer  receives  current  from  the 
alternator  A  (frequency  from  60  to  125  cycles)  when 
the  armature  of  the  transmitter  T'  rests  against  its  rear 
stop,  the  transmitter  being  actuated  by  the  current  from 
battery  b  through  the  key  K.  The  two  primary  windings 
of  the  receiving  transformer  t'  are  connected  in  the  line 
and  artificial  line  circuits,  their  secondary  windings  being 
properly  connected  in  series  to  the  phantoplex  relay  X, 
and  through  the  condenser  c.  This  phantoplex  relay  oper- 


QUADRUPLEX  TELEGRAPHY  105 

ates  a  sounder  (not  shown)  when  its  armature  rests  against 
its  rear  stop. 

When  the  key  K  is  raised,  as  shown,  an  alternating 
electromotive  force  is  induced  in  the  secondary  winding  of 
the  sending  transformer,  thereby  superimposing  an  alter- 
nating current  upon  whatever  steady  currents  traverse  this 
winding.  When  no  alternating  current  is  superimposed  on 
the  main  circuit  at  the  other  station  by  its  sending  trans- 
former (that  is,  the  distant  key  corresponding  to  K  is 
closed),  then  the  alternating  current  developed  at  /  divides 
equally  between  the  line  and  artificial  line  circuits.  The 
voltages  induced  in  the  secondary  windings  of  the  home- 
receiving  transformer  oppose  each  other,  and  do  not  cause 
the  attraction  of  the  armature  of  phantoplex  relay  X.  Its 
local  circuit  will  be  closed  and  the  sounder  actuated  —  the 
proper  condition,  for  the  distant  key  is  closed.  The  alter- 
nating current  that  traverses  the  line  wire  also  flows 
through  one  primary  winding  of  the  distant  receiving 
transformer,  no  current  flowing  through  its  other  primary 
winding.  As  a  result  the  distant  phantoplex  relay  will  be 
energized,  thereby  opening  its  local  circuit.  Thus  the  dis- 
tant phantoplex  sounder  will  not  be  energized  when  key  K 
is  raised.  Repeating  sounders  are  used  so  that  the  flutter- 
ing of  the  armatures  of  the  phantoplex  relays,  due  to  the 
alternating  currents  traversing  their  windings,  will  not 
affect  their  local  sounders. 

Condensers  ci,  c%  and  c$  provide  a  direct  path  past  the  re- 
sistances and  relay  windings  for  the  alternating  currents. 
The  alternating  currents  are  of  an  intensity  insufficient  to 
energize  the  quadruplex  relays. 


io6 


TELEGRAPH  ENGINEERING 


PROBLEMS. 

1.  In  the  battery  quadruplex  circuit  of  Fig.    2,   the  long-end 
battery  has  300  volts  and  the  short-end  has  100  volts,  the  internal 
resistance  being  2   ohms  per  volt.     Taking  the  resistance  of  the 
assumedly  perfectly-insulated  line  as  2000  ohms,  and  the  resistances 
of  the  polar  and  neutral  relays  as  400  and  200  ohms  respectively, 
calculate  according  to  the  method  of  §  2,  Chapter  II  (using  Rr  =  600), 
the  proper  resistance  of  the  artificial  line  when  both  short  ends  of 
the  battery  and  when  both  long  ends  of  the  battery  are  in  circuit. 

2.  With  the  artificial  lines  adjusted  to  2800  ohms  calculate  the 
currents,  in  milliamperes,  traversing  the  relay  coils  of  the  quadruplex 
circuit  of  Prob.  i  for  all  key  positions,  and  record  the  results  in 
tabular  form  as  indicated  below.    In  the  last  column  for  each  relay 
should  be  placed  the  equivalent  current  in  one  coil,  and  if  this  cur- 
rent is  of  sufficient  intensity  or  of  the  proper  direction  to  operate  the 
particular  relay,  this  figure  should  be  starred.    The  neutral  relays 
are  adjusted  so  that  a  current  greater  than  0.050  ampere  is  necessary 
for  their  operation. 


Keys  closed 
(Fig.  2.) 


none 
K 

K' 


KK' 
KK* 


KK'K2 


Relay  P 


Relay  R 


ll 

2£ 


Relay  P' 


Relay  R' 


QUADRUPLEX  TELEGRAPHY  107 

3.  If  the  two  3Oo-ohm  protective  resistances  of  the   single-gen- 
erator quadruplex  circuit  shown  in  Fig.  3  are  replaced  by  2oo-ohm 
resistances,  determine  the  proper  values  of  the  added  and  leak  re- 
sistances necessary  for  a  3  to  i  current  ratio. 

4.  Calculate  the  strengths  of  the  currents  in  the  artificial  line 
circuit  of  Prob.  3,  when  both  transmitter  armatures  are  released  and 
also  when  both  are  attracted. 

5.  Compute  the  terminal  resistance  of  the  Postal  Quadruplex, 
the  constants  of  which  are  given  in  §  4,  if  the  artificial  line  has  a 
resistance  of  2000  ohms. 

6.  Develop  the  diagram  of  connections  of  a  telegraph  line  circuit 
that  extends  from  city  A,  through  city  B,  to  city  C,  which  simulta- 
neously affords  two  channels  of  communication  (differential  duplex) 
between  cities  A  and  B  and  two  channels  (polar  duplex)  between 
cities  A  and  C. 


CHAPTER   IV 

AUTOMATIC  AND  PRINTING  TELEGRAPHY 

i.  Wheatstone  Automatic  Telegraphy.  —  When  rapid 
or  accurate  telegraphic  signalling  is  to  be  accomplished, 
automatic  transmitting  and  receiving  devices  are  availed  of, 
and  consequently  such  rapid  telegraphs  are  usually  called 
automatic  telegraph  systems.  The  Wheatstone  automatic 
system  has  been  most  extensively  used  and  permits  of 
satisfactory  telegraphic  transmission  at  speeds  up  to  400 
words  per  minute.  The  messages  to  be  transmitted  are 
perforated  in  specially  prepared  oiled  or  parchmentized 
paper  tapes  in  accordance  with  the  Morse  code,  and  these 
tapes  are  then  automatically  propelled  through  a  transmit- 
ter, which  is  really  a  high-speed  pole-changer,  driven  by 
springs  or  weights,  or,  more  modernly,  by  electric  motors. 
The  Wheatstone  transmitter  is  connected  in  the  line  circuit 
in  the  same  way  as  is  the  pole-changer  of  a  duplex  circuit. 
The  messages  are  received  at  the  distant  station  by  an 
inking  polarized  relay,  called  a  Wheatstone  recorder,  which 
records  the  message  in  the  Morse  code  on  a  tape,  as  is  done 
by  a  register. 

The  transmitting  tapes  are  prepared  by  means  of  three- 
key  mallet  perforators  or  keyboard  perforators,  and  appear 
as  in  Fig.  i,  which  shows  the  punching  for  the  word  " relay. " 
The  Morse  characters  are  also  shown,  the  letter  /  in  auto- 
matic telegraphy  being  written:  dot,  dash,  dash,  dash 
(Postal),  or  dot,  dot,  dash,  dash  (Western  Union),  instead  of 

108 


AUTOMATIC  AND   PRINTING  TELEGRAPHY 


109 


a  long  dash.  The  size  of  standard  perforator  tape  is  0.47 
inch  wide  and  from  4  to  5  mils  thick.  The  center  line  of 
holes,  or  guide  holes,  are  o.i  inch  apart  when  the  perforator 


O      00     O      00      O      C          OO          OO      OO 
ooooooooooooooooooooooooooo 
O     OO     O     O     O      O     O      O      O     OO      OO 


Fig.  i. 

is  properly  adjusted.  A  dot  appears  as  three  holes  in  a 
vertical  line,  a  space  appears  as  one  guide  hole,  and  a  dash 
appears  as  four  holes:  two  guide  holes  and  two  others,  one 
above  the  first  guide  hole  and  the  other  below  the  second 
guide  hole.  Longer  spaces  are  allowed  between  words, 
sentences  and  messages. 

A  mallet  perforator  with  interchangeable  punch-blocks 


Fig.  2. 


and  removable  punch-ends  is  shown  in  Fig.  2.  The  de- 
pression of  the  left  plunger  punches  a  dot,  the  center  plunger 
punches  a  space,  and  the  right  plunger  punches  a  dash. 


no 


TELEGRAPH  ENGINEERING 


The  punching  operator  uses  a  rubber-tipped  mallet  in 
each  hand  for  depressing  the  plungers.  The  plungers  are 
restored  by  springs  to  their  normal  position  after  each  de- 
pression, which  action  advances  the  tape  one  space  after 
the  depression  of  the  dot  or  space  plungers,  and  two  spaces 
after  depression  of  the  dash  plunger,  the  tape  feeding  being 
accomplished  by  a  small  spur-wheel  which  engages  in  the 
guide  holes. 

The  principle  of  operation  of  the  Wheatstone  high-speed 
transmitter  can  be  explained  with  the  aid  of  Fig.  3,  which 
illustrates  simplex  transmission  from  the  left-hand  to  the 


right-hand  station.  Only  those  mechanical  features  of  the 
transmitter  are  shown  which  serve  directly  in  the  capacity 
of  pole-changer.  The  transmitting  tape  /  is  moved  along 
over  a  slotted  platform,  in  the  direction  indicated  by  the 
arrow,  by  means  of  the  spur-wheel  w  which  engages  in  the 
guide  holes.  Another  wheel,  not  shown,  is  mounted  above 
the  spur-wheel  and  serves  to  press  the  tape  against  the 
platform.  Rods  /  and  b  pass  freely  through  a  guide  plate 
g  so  that  they  remain  respectively  in  ;line  with  the  front 
and  back  rows  of  holes,  and  are  spaced  longitudinally  so 
that  their  distance  apart  equals  the  distance  between  two 
adjacent  guide  holes.  The  rocking  beam  r  carries  out- 


AUTOMATIC  AND    PRINTING  TELEGRAPHY          III 

wardly-projecting  pins  p,  p,  which  limit  the  upward 
motion  of  the  rods  against  the  tendency  of  the  spring  s. 
The  eccentric  gear-wheel  k,  driven  at  any  desired  speed 
by  clockwork,  or  by  an  electric  motor,  causes  the  rocking 
beam  to  oscillate  through  a  small  arc  around  its  central 
pivot.  With  each  downward  movement  of  the  rod  b  the 
tape  moves  forward  one  space  or  the  distance  between  two 
successive  guide  holes.  The  motions  of  the  rods  /  and  b 
are  transmitted  to  the  pole-changer  C  by  means  of  the 
cranks,  rods  and  the  ivory  collets  c,  c.  The  function  of  the 
jockey-roller  /  is  to  hasten  the  movements  of  the  pole- 
changer  and  to  insure  steady  contacts. 

If  the  transmitter  is  set  in  operation  without  carrying  a 
tape,  the  rise  and  fall  of  the  rods  will  be  unhindered,  and 
every  time  the  front  rod  /  is  in  its  upper  position,  the  posi- 
tive terminal  of  the  battery  B  is  connected  to  the  line 
while  its  negative  terminal  is  grounded,  and  every  time 
the  back  rod  b  is  in  its  upper  position  (as  in  Fig.  3)  the 
negative  battery  (or  generator)  terminal  is  joined  to  the 
line.  Thus  the  battery  is  reversed  with  every  half  oscil- 
lation of  the  rocker  arm  when  the  transmitter  is  operating 
idly. 

These  current  reversals  cause  the  armature  of  the  polar- 
ized relay  P  to  oscillate  simultaneously,  which  motion  is 
translated  to  the  printing  wheel  shaft  a  that  is  kept  re- 
volving by  means  of  the  gear-wheel  d.  Whenever  the 
positive  battery  terminal  is  joined  to  the  line  at  the  trans- 
mitter, the  direction  of  the  current  through  the  polarized 
relay  is  such  as  to  hold  the  printing  wheel  i  against  the 
inking  wheel  h  which  dips  in  the  ink  reservoir  e.  And 
when  the  negative  battery  terminal  is  connected  to  the 
line,  the  current  direction  is  such  as  to  press  the  inking 


112  TELEGRAPH  ENGINEERING 

wheel  almost  against  the  moving  receiving  tape  tr .  These 
currents  are  called  spacing  and  marking  currents  respec- 
tively. Thus,  when  the  transmitter  operates  without  tape, 
a  succession  of  dots  appears  on  the  receiving  tape. 

At  the  instant  represented  in  the  figure  rod  b  has  passed 
through  the  tape,  thereby  sending  a  marking  current  and 
causing  the  printing  wheel  to  press  almost  against  the 
receiving  tape  and  leave  an  ink  mark  thereon.  The  rock- 
ing beam  then  draws  down  rod  b  and  allows  rod/  to  rise; 
meanwhile  the  tape  has  moved  forward  one  space.  In 
this  case  the  signal  is  a  dot,  and  consequently  rod  /  in  its 
upward  motion  meets  the  front  or  lower  hole  and  so  passes 
through  it.  The  complete  transit  of  this  rod  causes  the 
shifting  of  the  pole  changer  C  and  the  sending  of  a  spacing 
current;  consequently  the  printing  wheel  i  is  withdrawn 
from  the  receiving  tape  to  the  inking  wheel.  A  dot  is 
printed  on  the  receiving  tape. 

If,  instead,  the  signal  were  a  dash,  the  upward  movement 
of  rod  /  would  be  arrested  by  the  tape,  because  in  a  dash 
perforation  there  is  no  lower  hole  in  line  with  the  upper 
hole.  As  a  consequence,  the  pole-changer  would  not  be 
operated.  Tracing  the  operation  further,  the  upward 
movement  of  rod  b  would  also  be  restricted,  but  the  next 
upward  movement  of  the  other  rod  /  would  cause  it  to  pass 
through  the  lower  hole,  which  movement  reverses  the  pole- 
changer.  The  time  elapsing  since  the  last  reversal  is 
sufficient  to  form  a  dash  signal  on  the  receiver  tape.  It 
will  be  observed  that  the  current  pulse  for  a  dash  signal 
is  of  the  same  direction  as  for  a  dot  signal,  but  three  times 
as  long.  For  relatively  low  transmission  speeds  the  signals 
may  be  read  from  a  sounder  connected  to  the  local-circuit 
contacts  of  the  receiving  relay. 


AUTOMATIC   AND   PRINTING  TELEGRAPHY  113 

Fig.  4  shows  an  automatic  transmitter  made  by  Muir- 
head  &  Co.,  Ltd.,  for  cable  signalling.  It  is  provided  with 
a  local  pole-changer,  speed  regulator,  speed  indicator,  and 
a  switch  for  shifting  connections  from  transmitter  to  hand- 
key  sending,  which  at  the  same  time  lifts  the  paper  wheel 
off  the  spur-wheel.  The  mechanical  devices  of  the  trans- 


Fig.  4- 

mitter  are  somewhat  different  from  those  shown  in  Fig.  3, 
but  have  the  same  function. 

The  connections  of  the  Wheatstone  automatic  system  for 
duplex  operation  are  indicated  in  Fig.  5,  which  shows  only 
the  electrical  features  at  one  station.  The  connections  are 
those  of  the  polar  duplex,  already  described,  with  a  choice 


TELEGRAPH   ENGINEERING 


of  pole-changers.  When  the  switch  S  is  to  the  left  as 
shown,  the  automatic  transmitter  C  is  in  circuit,  and  when 
this  switch  is  shifted  to  the  right,  the  pole-changer  Ci  con- 
trolled by  the  key  K  is  in  circuit.  The  Wheatstone  recorder 
P  is  immune  from  the  movements  of  the  home  transmitting 
devices  C  or  Ci  and  will  only  respond  to  the  operation  of 


either  the  distant  automatic  transmitter  or  the  distant 
manually-operated  pole-changer.  The  Wheatstone  system 
is  almost  invariably  operated  duplex. 

Repeaters  for  use  with  the  Wheatstone  automatic  system 
resemble  polar  direct-point  duplex  repeaters  (§  10,  Chap.  II) 
thereby  dispensing  with  automatic  transmitters  at  the 
repeating  station  for  through  operation.  A  Wheatstone 
recorder  may  be  introduced  at  the  repeater  as  a  leak  relay 
to  enable  the  attendant  to  discern  the  character  of  the 
signals  passing  through  the  repeater. 

The  system  described  has  been  used  by  the  Western 
Union  Telegraph  Company  for  many  years.  The  auto- 
matic system  used  by  the  Postal  Telegraph- Cable  Company 
differs  herefrom  in  the  reception  of  the  signals.  It  em- 
ploys instead  of  the  inking  Wheatstone  recorder,  an  elec- 
tromagnetic punch,  or  reperforator,  invented  by  d'Humy. 

The  reperforator  punches  characters  in  a  moving  tape 
somewhat  similar  to  those  of  the  transmitting  tape.  If  the 


AUTOMATIC  AND   PRINTING    TELEGRAPHY          115 

completed  receiving  tape  be  passed  slowly  through  a  repro- 
ducer, whose  speed  is  in  control  of  the  receiving  operator, 
the  messages  can  be  read  by  ear  and  simultaneously  copied 
by  hand  or  on  a  typewriter.  The  punches  of  the  reper- 
forator are  adjusted  to  travel  over  a  very  short  distance, 
and  their  motion  is  rendered  rapid  by  strong  retractile 
springs  and  by  a  series  condenser  in  the  punch  magnet  cir- 
cuits. Such  small  and  rapid  motion  of  the  punches  com- 
bined with  a  tape  take-up  device  are  the  essential  features 
of  the  reperforator,  for  they  shorten  the  time  of  tape 
stoppages  during  punching  and  compensate  for  these  stop- 
pages respectively,  thereby  preventing  tearing  of  the  tapes. 

2.  Ticker  Telegraphs.  —  A  ticker  telegraph  system  com- 
prises a  transmitter  and  a  number  of  receiving  instruments, 
called  tickers,  which  print  the  messages  in  ordinary  type 
on  paper  tape  as  they  are  received.  The  various  ticker 
systems  for  the  dissemination  of  news  and  stock  quotations 
differ  widely  in  the  mechanical  construction  of  instruments, 
but  the  fundamental  operating  principles  are  not  very 
different. 

A  schematic  diagram  of  a  transmitter  with  one  ticker 
of  such  a  tape-printing  system  is  given  in  Fig.  6.  The 
transmitter  consists  of  a  shaft  5  driven  by  a  constant- 
speed  motor  M  through  a  friction  clutch  k.  Mounted  on 
this  shaft  is  a  current-reversing  commutator  c,  formed  by 
a  pair  of  metal  crown-shaped  wheels  which  are  fitted 
into  but  insulated  from  each  other.  The  wheels  connect 
through  brushes  with  the  negative  and  positive  terminals 
respectively  of  generators  D  and  Z>',  the  other  generator 
terminals  being  grounded.  The  shaft  also  carries  an 
escapement  wheel  e,  and  a  contact  arm  a  which  passes 


n6 


TELEGRAPH  ENGINEERING 


over  the  contact  points  located  on  the  contact  disk  C. 
The  escapement  is  controlled  by  an  electromagnet  m 
through  the  keyboard  K.  Upon  the  depression  of  any 
key  no  current  from  the  battery  B  will  flow  through  the 
electromagnet  until  the  contact  arm  a  reaches  the  contact 
stud  corresponding  to  the  key  depressed.  At  that  instant 
the  armature  of  magnet  m  will  be  attracted,  thereby 
arresting  the  rotation  of  the  shaft  and  commutator.  Thus 
the  shaft  is  stopped  at  a  particular  place  for  each  depressed 
key. 

At  the  receiver  the  type-wheel  T  is  rotated  by  clock- 


Fig.  6. 


work  through  the  gear-wheel  g,  but  this  rotation  is  con- 
strained by  means  of  the  escapement  wheel  w.  The  arma- 
ture of  polarized  relay  P  controls  this  escapement  wheel. 
The  rear  end  of  the  armature  of  printing  relay  R,  when 
this  instrument  is  operated,  presses  the  tape,  which  moves 
over  the  armature,  against  the  type-wheel;  consequently 
that  letter  will  be  printed  on  the  tape  which,  at  the  mo- 
ment of  operation  of  the  relay  R,  is  in  the  lowest  position. 
If  n  characters  are  to  be  employed  in  transmission,  there 
must  be  n  keys  on  the  keyboard,  n  notches  on  the  escape- 


AUTOMATIC  AND   PRINTING  TELEGRAPHY          117 

ment  wheel  e,  n  contact  studs  on  C  and  n  segments  on  the 
commutator  c\  the  commutator  brushes  and  the  contact 
arm  a  being  properly  aligned  with  respect  to  the  notches 
on  the  escapement  wheel.  Thus,  depressing  any  given  key 
will  always  stop  the  shaft  at  the  same  place.  At  the 
receiver  there  are  also  n  characters  on  the  type-wheel  and 
n  teeth  on  the  escapement  wheel. 

In  operation,  when  no  keys  are  depressed,  the  trans- 
mitter shaft  revolves  uniformly  and  the  current  supplied 
to  the  line  is  periodically  altered  in  direction  by  the  com- 
mutator. This  reversal  of  polarity  occurs  so  rapidly  that 
the  current  in  relay  R  never  reaches  a  value  sufficient  to 
cause  the  attraction  of  its  armature  before  the  next  re- 
versal takes  place,  consequently  the  rear  end  of  this 
armature  does  not  press  the  tape  against  the  type-wheel. 
However,  the  alternating  current  traversing  the  sensitive 
polarized  relay  P  causes  its  armature  to  shift  its  position 
with  each  reversal  in  polarity,  thereby  operating  the  escape- 
ment. One  revolution  of  the  transmitter  shaft  produces 
n  current  reversals  and  the  escapement  wheel  at  the  re- 
ceiver moves  through  n  notches,  or  one  revolution.  It  is 
evident,  then,  that  if  the  type-wheel  is  started  with  its 
characters  in  a  certain  position,  it  will  always  remain 
during  proper  operation  in  the  same  relative  position  with 
respect  to  the  transmitter  shaft.  The  proper  position  of. 
the  type-wheel  is  such  that  the  letter  a  will  be  in  the 
printing  position  when  the  a-key  of  the  transmitting  key- 
board is  depressed. 

Upon  the  depression  of  any  key  the  motion  of  the  shaft 
and  commutator  will  be  momentarily  arrested.  This 
stopping  is  permitted  by  the  friction  clutch  without  affect- 
ing the  rotation  of  the  motor.  During  this  instant  the 


Il8  TELEGRAPH   ENGINEERING 

current  ceases  to  alternate  in  direction,  and  relay  R  is 
enabled  to  attract  its  armature.  This  action  presses  the 
tape  against  the  type-wheel,  thus  printing  the  character 
corresponding  to  the  key  that  is  depressed  at  the  trans- 
mitter keyboard.  As  the  armature  resumes  its  former 
position  through  the  intervention  of  spring  s,  the  tape  is 
moved  forward  one  space  by  clockwork  and  is  ready  for 
the  printing  of  the  next  character. 

The  system  just  described  is  known  as  a  single- wire  and 
single  type-wheel  ticker  system.  To  avoid  spelling  figures, 
which  occur  very  frequently  in  stock  quotations,  figures 
and  fractions  should  also  be  provided  on  the  keyboard 
and  type-wheel.  Adding  to  the  26  letters  of  the  alphabet 
10  figures  and  say  7  fractions  would  increase  the  size  of 
the  wheel  and  would  materially  decrease  the  speed  of  oper- 
ation. Instead,  it  is  customary  to  use  two  type- wheels 
on  the  same  ticker-shaft  and  adjacent  to  each  other,  one 
containing  letters  and  a  couple  of  dots,  and  the  other  con- 
taining figures  and  fractions.  As  the  numbers  of  charac- 
ters on  both  type-wheels  should  be  identical,  the  fractions 
may  be  repeated  and  the  still-existing  deficiency  may  be 
made  up  by  dots.  A  ticker  so  equipped  is  called  a  two- 
wheel  ticker. 

In  two-wheel  tickers  provision  must  be  made  for  shifting 
either  the  type-wheels  or  the  tape  in  order  to  print  from 
either  wheel.  This  shifting  is  accomplished  electromag- 
netically  in  a  variety  of  ways  in  the  various  ticker  systems. 
For  fast  working  an  additional  wire  is  generally  used  for 
the  current  which  actuates  the  shifting  magnet,  thus  neces- 
sitating two  line  wires  to  each  ticker. 

Should,  for  any  reason,  the  type-wheel  of  a  ticker  be 
thrown  out  of  step  with  the  transmitter,  as  may  occur 


AUTOMATIC   AND   PRINTING  TELEGRAPHY  119 

upon  sticking  of  the  escapement  wheel  or  momentary  inter- 
ruptions of  the  line  wire,  a  jumble  of  letters  on  the  tape  will 


Fig.  7. 


result.   Automatic  devices,  termed  unison  devices,  are  availed 
of  to  bring  the  tickers  back  into  step  whenever  desired. 


Fig.  8. 


Generators  are  now  more  frequently  employed  in  the 
operation  of  ticker  systems  than  batteries,  the  generator 


I2O 


TELEGRAPH  ENGINEERING 


leads  being  provided  with  fuses  and  protective  resistances. 
Condensers  are  also  used  in  these  systems  for  the  elimina- 
tion of  sparking  at  the  transmitter  contacts. 

The  appearance  of  the  ticker  used  by  the  Stock  Quota- 
tion Telegraph  Company  in  New  York  is  shown  in  Fig.  7. 


Fig.  9. 

It  has  8  ohms  resistance  and  requires  about  0.65  ampere 
for  operation.  Figs.  8  and  9  show  respectively  the  key- 
board and  motor-driven  transmitter  used  at  the  central 
station  of  a  ticker  system.  The  cost  of  ticker  service  is 
about  $20  per  month.  Fac-simile  reproductions  to  full 


.SUPREME. COURT. OF. THE. U.S. 


.80 


SP 


U 


.9!  | 

.700.833 

.147 

Fig.  10. 


scale  of  the  received  tapes  of  a  news  ticker  and  a  stock 
quotation  system  are  given  in  Fig.  10;  the  significance  of 


AUTOMATIC   AND   PRINTING  TELEGRAPHY          121 

the  stock  abbreviations  on  the  lower  tape  being  BO  =  Balti- 
more &  Ohio,  SP  =  Southern  Pacific,  and  U  =  Union 
Pacific. 

3.   The   Barclay  Page-printing  Telegraph   System.  - 

The  Barclay  printing  telegraph  system  is  now  extensively 
used  by  the  Western  Union  Telegraph  Company,  and  com- 
prises a  keyboard  perforator,  an  automatic  transmitter, 
and  a  receiving  polarized  relay  which  repeats  the  arriving 

BARCLAY  PRINTING  TELEGRAPH  CODE 

A     —  ^_.  „  O  9  _  -      _ 

B    @  -      —      _  P  O  _      __  _ 

C      :  _  -  _  Q  I  _      _  _ 

D$  _      __  R  4  p.  _      _ 

E      3  ___  S  #  __  - 

T     X  __      -  T  5  ... 

G&         __    _  u    T  _-_ 

H     *  -__  V      J  —  «_      . 

I      8  ___  W     3  _      .__ 

J       '  .  --      -  XI  _      .      - 

Kf  ---  Y6  _._ 

L)  .      __  Z      "  __      _ 


ce 
Type  Shift  __      -      ^^  Carriasre  Return  ^      ^^      mm^ 


---  , 

Space  -.  .  «  Paper  Feed. 


signals  into  a  set  of  local  relays  which  control  the  opera- 
tions of  the  printing  magnets,  the  received  message  being 
directly  printed  in  page  form  on  message  blanks.  This 
system  may  be  operated  successfully  through  several  re- 
peaters. Its  capacity  is  about  100  words  per  minute  over 
lines  1000  miles  long. 

Transmitting  Apparatus.    Messages  to  be  transmitted 
are  first  perforated  in  prepared  paper   tapes,  exactly  as 


122  TELEGRAPH  ENGINEERING 

in  the  Wheatstone  automatic  telegraph  system  described  in 
§  i,  only  a  different  code  is  employed.  The  code  used  in 
the  Barclay  system  has  three  elements  for  each  character 
and  these  are  separated  from  each  other  by  short  or  long 
spaces,  as  shown  on  the  preceding  page.  The  spaces  be- 
tween the  various  words,  figure  groups,  etc.,  are  formed 
by  three  closely-spaced  dots.  Thus,  the  perforations  in 
the  transmitting  tape  for  the  word  " relay"  would  appear 


>oo    oo       o    oo    o    o    oo      o    oo    o      o    o    ooo 

lOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 

>OO     O     O     O      O     OO     OOO         OOO         OOO     OOO 


RELAY 
Fig.  II. 

as  in  Fig.  n  (compare  with  Fig.  i  showing  perforations 
according  to  Morse  code). 

The  Kleinschmidt  perforator,  now  largely  used  with  the 
Barclay  page-printer,  is  shown  in  Fig.  12,  and  is  a  purely 
mechanical  device  for  punching  the  tape,  but  derives  its 
motive  power  from  an  electric  motor.  All  the  perforations 
representing  a  letter,  figure  or  other  character  on  the  tape, 
as  well  as  their  proper  spacing,  are  produced  by  a  single 
depression  of  the  key.  After  this  depression,  the  tape  is 
advanced  a  distance  commensurate  with  the  space  occupied 
by  the  letter  or  figure.  After  about  60  letters  are  punched 
an  indicator  lamp  illuminates  giving  a  warning  that  the 
end  of  a  line  (on  the  receiving  page)  is  approaching.  The 
pointer,  which  indicates  the  number  of  letters  perforated, 
is  returned  to  zero  by  the  depression  of  the  indicator  key 
before  the  limiting  number  of  75  characters  have  been 
prepared. 

The  automatic  transmitter  used  with  the  Barclay  print- 


AUTOMATIC   AND   PRINTING  TELEGRAPHY  123 


Fig.  12. 


ing  system  is  a  Wheatstone  transmitter,  or  high-speed  pole- 
changer,  as  described  in  §  i.  A  front  elevation  of  the  upper 
portion  of  this  transmitter  is  shown  in  Fig.  13,  wherein 
most  of  the  letters  refer  to  the  same  parts  as  in  Fig.  3. 


Fig.  13. 


124  TELEGRAPH   ENGINEERING 

The  pole-changer  contacts  are  shown  at  k  and  fe,  and  con- 
nect respectively  with  the  negative  and  positive  terminals 
of  the  generators.  In  operation  the  adjustment  of  the 
rods  /  and  b  must  be  very  precise,  and  is  effected  by  the 
screws  e  and  e' '.  When  the  switch  5  is  thrown  to  the  left 
the  paper  wheel  P,  which  is  shown  bearing  upon  the  tape, 
is  raised  out  of  engagement  with  the  spur-wheel  w,  thereby 
halting  the  progression  of  the  tape.  A  local  pole-changer 
for  hand  signalling  is  located  in  the  base  of  the  automatic 
transmitter.  In  practice,  when  the  transmitter  operates 
without  tape,  from  40  to  70  current  reversals  take  place  per 
second. 

When  the  front  rod  /  is  at  the  upper  end  of  its  travel  the 
positive  generator  terminal  is  joined  to  the  line,  and  when 
the  other  rod  is  in  a  similar  position  the  negative  generator 
terminal  connects  to  the  line.  Thus,  for  each  letter  there 
are  six  current  pulses,  three  positive  and  three  negative, 
and  the  code  is  so  arranged  that  there  is  at  least  one  long 
current  pulse  among  the  first  five,  either  positive  or  nega- 
tive, per  character.  In  the  letter  R  (•  —  "),  for  example, 
these  current  pulses  have  the  following  sequence:  short 
negative,  short  positive,  long  negative,  long  positive,  short 
negative,  long  positive,  the  last  pulse  corresponding  to  the 
space  between  this  and  the  next  following  letter.  The 
significance  of  the  code  elements  are  therefore: 

dot  =  short  negative  current; 

dash  =  long  negative  current; 

short  space  =  short  positive  current; 
long  space     =  long  positive  current. 

Receiving  Apparatus.  —  The  current  impulses  sent  out 
by  the  transmitter  are  received  by  a  differentially-wound 


AUTOMATIC   AND   PRINTING   TELEGRAPHY 


125 


polarized  relay  of  special  construction  to  render  it  quick 
acting.  To  attain  this  end,  its  magnetic  circuit  has  several 
air  gaps,  the  moving  element  has  a  small  moment  of 
inertia,  and  the  two  coils  of  each  winding  are  connected  in 
parallel.  The  series  resistance  of  each  winding  is  150  ohms. 
A  top  view  of  this  relay  is  shown  in  Fig.  14,  in  which  a  is 


Fig.  I4. 

the  armature  tongue,  e  is  the  separately-excited  energizing 
coil  which  takes  the  place  of  the  usual  permanent  magnet, 
m,  m  are  the  main  winding  bobbins  with  the  pole-pieces  p, 
p]  c,  c  are  the  platinum  contacts,  and  k  is  the  knurled 
screw  which  moves  the  bridge  b  carrying  these  contacts. 

The  connections  of  the  main  line  and  artificial  line  cir- 
cuits of  automatic  duplex  apparatus  as  arranged  in  the 


126 


TELEGRAPH  ENGINEERING 


Fig.  15. 


Barclay  printing  telegraph  system  are  shown  in  Fig.  15 
for  one  terminal  station.  In  the  figure,  C  is  the  pole- 
changer,  D,  D  are  the  generators,  P  is  the  polarized  relay 

with  its  coils  connected  in 
parallel,  AL  is  the  artificial 
line,  and  g  is  a  differential 
galvanometer  which  aids  in 
line  balancing.  Repeaters 
for  use  with  this  system  re- 
semble polar  duplex  direct- 
point  repeaters. 

The  main-line'  relay  con- 
trols through  the  intervention  of  a  " printer  relay,"  a  " sepa- 
rator relay,"  an  " escapement  magnet"  and  a  " sunflower" 
distributing  switch,  the  operation  of  five  "  distributing 
relays"  with  multiple  contact  points,  which  in  turn  control 
the  operation  of  32  "printer"  magnets.  The  actuation  of 
the  distributing  relays,  as  dependent  upon  the  nature  of 
the  received  current  impulses,  may  be  studied  with  the 
aid  of  diagram  Fig.  16,  in  which  the  various  intermediate 
devices  mentioned  are  indicated. 

The  separator  relay  is  a  neutral  relay  which  is  adjusted 
to  be  responsive  only  to  long  current  impulses  in  either 
direction.  The  escapement  magnet  is  a  polarized  relay 
which  controls  the  movement  of  the  escape  wheel.  This 
wheel  has  45  teeth  and  is  mounted  on  the  same  shaft  as 
the  unison  wheel  with  15  teeth,  the  shaft  tending  to  rotate 
under  the  influence  of  an  electric  motor.  The  six  current 
pulses  of  each  letter  or  character,  alternately  negative 
and  positive,  that  traverse  the  escapement  magnet  cause 
the  escape  wheel  to  turn  through  a  distance  corresponding 
to  3  teeth  and  the  unison  wheel  through  a  distance  of  one 


AUTOMATIC  AND   PRINTING  TELEGRAPHY          127 

tooth.  As  the  unison  wheel  turns,  its  teeth  successively 
butt  against  the  toes  of  the  six  pivoted  levers  marked 
i,  2,  3,  4,  5  and  6;  thereby  establishing  connections  with 
the  five  distributing  relays  and  the  sixth  pulse  or  " final" 
relay.  However,  the  circuits  of  the  five  distributing  relays 
are  only  completed  when  the  armature  of  the  separator  relay 
is  on  its  front  contact,  which  occurs  only  when  a  long  cur- 
rent pulse  traverses  its  winding. 

Suppose  the  letter  R  is  being  received;  the  impressed 
pulses  are:  short  — ,  short  +,  long  — ,  long  -f,  short,— 
and  long  +.  Fig.  16  shows  the  armature  positions  during 
the  first  pulse.  The  armatures  of  the  line  and  printer 
relays  are  respectively  on  their  right  and  left  contacts,  the 
armature  of  the  separator  relay  is  not  attracted,  and  the 
armature  of  the  escapement  magnet  is  toward  the  right. 
The  unison  wheel  has  turned  through  one-sixth  the  distance 
between  two  teeth,  thereby  causing  a  tooth  to  engage  the 
toe  of  pivoted  lever  i.  But  inasmuch  as  the  circuit  of 
distributor  relay  i  is  interrupted  at  the  separator  relay 
armature,  the  closing  of  its  circuit  at  the  sunflower  does 
not  cause  the  operation  of  relay  i,  which  remains  inop- 
erative until  the  end  of  the  cycle  of  current  pulses  for  the 
selected  letter.  During  the  second  pulse  the  armatures  of 
the  line  and  printer  relays  and  of  the  escapement  magnet 
will  be  in  their  opposite  positions,  and  the  armature  of  the 
separator  relay  will  still  remain  unattracted.  Therefore  the 
completion  of  the  circuit  of  relay  2  at  the  sunflower  does 
not  cause  the  operation  of  relay  2.  The  third  pulse  is  of 
dash  duration,  so  the  separator  relay  is  capable  of  attract- 
ing its  armature  by  current  supplied  by  generator  D.  The 
escape  wheel  has  moved  another  half  notch,  bringing  a 
tooth  of  the  unison  wheel  in  engagement  with  the  toe  of 


128 


TELEGRAPH   ENGINEERING 


SEPARATOR 
RELAY 


IT  T 


ESCAPEMENT 
MAGNET 


5  32  PRINTERS  MAGNETS 


Fig.  16. 


AUTOMATIC  AND   PRINTING  TELEGRAPHY          129 

pivoted  lever  3.  Relay  3  will  therefore  be  operated  and 
remain  so  until  the  expiration  of*  the  remaining  three- 
current  pulses.  The  fourth  pulse  likewise  causes  the  oper- 
ation of  distributor  relay  4.  As  the  fifth  pulse  is  of  short 
duration,  relay  5  will  not  be  actuated.  Thus  for  the  letter 
R,  relays  3  and  4  are  operated  and  close  local  circuits  (not 
shown  in  this  figure)  which  hold  all  printer  magnets  open 
except  that  which  prints  the  letter  R,  as  will  be  described 
subsequently.  The  closing  of  sunflower  contact  6  causes  a 
current  pulse  always  of  long  duration,  since  it  represents 
the  interval  between  letters,  to  flow  from  the  generator  Dr 
through  the  rear  spring  contact  of  the  final  relay,  through 
the  particular  printer  magnet  corresponding  to  the  letter 
R,  which  places  this  letter  in  the  printing  position,  and 
through  the  trip  magnet  which  causes  the  type-wheel  to 
come  in  contact  with  the  message  blank.  Since  the  estab- 
lishment of  this  sixth  pulse  the  armature  of  the  final  mag- 
net has  been  moving  forward  due  to  the  current  through 
its  winding.  This  movement  soon  opens  the  circuit  of 
the  printer  and  trip  magnets,  but  is  adjusted  not  to  do  so 
until  the  proper  printing  of  the  desired  letter  is  accomplished. 
Immediately  after  opening  this  circuit,  the  armature  comes 
in  contact  with  its  front  stop,  thereby  establishing  a  current 
through  the  left-hand  or  " reset"  coils  of  the  five  distribut- 
ing relays,  which  is  in  a  direction  to  cause  the  armatures 
of  the  relays  previously  energized  to  resume  their  normal 
position  on  the  left,  in  readiness  for  the  next  letter. 

The  distributing  system,  whereby  a  particular  printer 
magnet  out  of  thirty-two  is  selected  by  means  of  the  five 
distributing  relays,  is  shown  in  Fig.  1 7 .  Relay  i  is  equipped 
with  two  contacts,  relay  2  with  four  contacts,  relay  3  with 
eight  contacts,  relay  4  with  sixteen  contacts,  and  relay  5 


130 


TELEGRAPH   ENGINEERING 


with  thirty-two  contacts.    The  small  contact  levers  shown 
in  the  figure  are  insulated  from  each  other. 
The  sequence  of  the  long-current  pulses  in  any  letter  or 


Fig.  17. 


character  determines  the  relay  or  group  of  relays  that  will 
be  operated  in  the  selection  of  the  particular  printer  mag- 
net. In  the  transmission  of  letter  R  the  third  and  fourth 
relays  are  operated,  causing  their  armatures  to  move  to- 


AUTOMATIC  AND  PRINTING  TELEGRAPHY          131 

ward  the  right.  This  condition  is  represented  in  Fig.  17, 
and  it  is  evident  that  the  only  printer  magnet  circuit  that 
is  closed  is  that  which  places  the  letter  R  in  the  printing 
position,  the  direction  of  current  flow  being  indicated  by 
the  arrows.  Current  simultaneously  traverses  the  trip 
magnet  which  urges  the  type-wheel,  now  rotated  to  its 
proper  position,  against  the  paper,  causing  the  printing 
of  the  letter  R  thereon.  In  a  similar  manner  the  selection 
of  the  printer  magnet  for  any  other  letter  or  character  is 
accomplished. 

The  printing  of  the  " upper-case"  characters,  given  in 
the  second  column  of  the  Barclay  printing  code,  is  accom- 
plished by  raising  the  type- wheel,  which  carries  56  char- 
acters grouped  in  two  rows,  so  that  the  upper-case  letters 
are  brought  into  the  printing  line.  Raising  the  type- 
wheel  is  done  by  the  type-shift  magnet  T  and  its  assisting 
magnet  A,  and  the  type- wheel  remains  raised  until  a 
" space"  is  transmitted,  which  lowers  the  type-wheel  (if 
raised)  through  the  operation  of  the  type-release  magnet 
R,  as  shown  also  in  Fig.  17.  As  the  sixth  current  pulse  is 
of  insufficient  duration  to  cause  the  proper  actuation  of 
the  type-shift  magnet  T,  the  assisting  magnet  A  keeps  the 
circuit  of  the  other  closed  until  the  type-wheel  is  raised. 
Since  magnets  T  and  A  are  connected  in  parallel,  both 
will  be  magnetized  when  the  sixth  current  pulse  of  the 
type-shift  group  passes  through  their  coils.  Magnet  A 
attracts  its  armature  and  causes  current  to  flow  from  gener- 
ator D  through  the  coils  of  the  type-shift  magnet  until 
the  armature  of  this  magnet  is  at  the  end  of  its  travel. 
When  this  occurs  the  windings  of  both  magnets  are  short- 
circuited,  the  assisting  magnet  releasing  its  armature, 
thereby  opening  the  circuit  of  generator  D.  The  armature 


132  TELEGRAPH   ENGINEERING 

of  the  type-shift  magnet  is  held  down  by  the  catch  c  engag- 
ing the  pin  p;  consequently  the  type-wheel  is  maintained 
in  its  upper  position  for  the  printing  of  upper-case  letters 
until  released  by  the  attraction  of  catch  c  by  the  type- 
release  magnet  R,  which  operates  on  the  reception  of  the 
" space"  character. 

Shifting  of  the  paper  for  line  spacing  is  accomplished  by 
the  paper-feed  magnet  which  is  actuated  by  the  sixth  pulse 
following  5  dash  current  pulses.  Its  operation  is  identical 
with  that  of  the  type-shift  magnet,  being  assisted  also  by 
an  auxiliary  magnet,  not  shown  in  the  diagram. 

The  carriage,  holding  the  paper  upon  which  the  message 
is  printed,  is  returned  to  the  starting  position  by  means 
of  the  carriage-return  magnet,  the  mechanism,  as  before, 
not  being  shown  in  the  figure.  When  the  armature  of  this 
magnet  is  attracted,  causing  the  return  of  the  carriage, 
the  circuit  of  the  final  relay  is  opened  at  the  normally- 
closed  contacts  m.  As  a  result,  the  current  through  the 
final  relay  is  interrupted  before  its  armature  spring  breaks 
contact  with  its  rear  stop,  through  which  current  continues 
to  flow  from  generator  Df  to  energize  the  carriage-return 
magnet.  The  instant  the  carriage  arrives  at  its  starting 
position,  the  circuit-breaker  B  opens  the  circuit  of  the 
carriage-return  magnet,  which  in  releasing  its  armature, 
completes  at  m  the  circuit  of  the  final  relay,  thereby  per- 
mitting this  relay  to  reset  the  distributing  relays. 

Reverting  to  Fig.  16,  the  lever  of  the  synchronizing  mag- 
net is  seen  to  act  upon  the  unison  wheel.  The  function  of 
this  magnet  is  to  restore  f  the  unison  wheel  to  the  zero 
position,  if,  for  any  reason,  it  gets  out  of  step  with  the  in- 
coming current  pulses.  The  winding  of  this  instrument, 
which  is  of  the  polarized  type,  is  such  that  its  permanent 


AUTOMATIC  AND   PRINTING  TELEGRAPHY  133 

magnetization  is  opposed  by  negative  current  pulses  and 
assisted  by  positive  current  pulses.  Since  the  armature 
of  this  magnet  is  adjusted  not  to  operate  on  short-current 
pulses,  only  long  positive  current  pulses  bring  the  synchro- 
nizer into  action.  Such  pulses  occur  in  some  letters,  and 
occur  invariably  at  the  end  of  each  letter  or  character. 
In  proper  operation,  the  hook  on  the  synchronizer  lever 
rests  in  spaces  between  the  teeth  of  the  unison  wheel,  and 
would  interfere  with  its  motion  at  the  end  of  each  letter 
were  not  the  synchronizer  magnet  energized  at  that  instant 
by  a  long  positive  pulse.  Should  any  pulses  of  a  letter  be 
lost,  this  magnet  would  restore  synchronism  upon  the 
reception  of  the  next  following  long  positive  current  pulse. 

4.  Other  Printing  Telegraph  Systems.  —  The  Mor- 
krum  page-printing  telegraph  system  is  also  used  at 
present  both  by  the  Western  Union  Telegraph  and  Postal 
Telegraph-Cable  Companies.  The  Baudot  tape-printing 
system  is  extensively  used  abroad,  the  system  being 
operated  simplex,  duplex  or  multiplex.  The  Hughes  tape- 
printing  system  is  largely  employed  in  Europe,  about  3000 
instruments  being  now  in  use.  The  Rowland  multiplex 
and  the  Wright  page-printing  systems  were  for  a  time  used 
on  some  circuits  of  the  Postal  Company.  The  Burry  page- 
printing  telegraph  is  used  by  the  Stock  Quotation  Tele- 
graph  Company  for  disseminating  general  and  financial 
news  in  New  York  City  and  vicinity. 

Many  other  systems  have  been  invented  and  are  now 
used  more  or  less  here  and  abroad  for  the  direct  printing 
of  the  received  messages,  among  which  may  be  mentioned 
the  systems  of  Munier,  Murray,  Essick,  Dean,  Creed, 
Siemens,  Kinsley  and  Buckingham,  the  last  being  the  fore- 


134  TELEGRAPH   ENGINEERING 

runner  of  the  Barclay  printing  system,  herein  described. 
Multiplex  page-printing  telegraph  systems  will  be  consid- 
ered in  Chap.  VI. 

PROBLEMS 

1.  Show  the  appearance  of  a  transmitting  tape  for  automatic 
telegraphic  transmission  with  perforations  representing   the  word 
"Wheatstone." 

2.  How  many  words  may  be  telegraphically  transmitted  in  one 
direction  over  a  wire  by  the  Wheatstone  automatic  system  in  6  hours 
if  the  perforated  tape  is  passed  through  the  transmitter  at  the  rate 
of  4  words  per  second?    Allow  two  per  cent  for  idleness  in  changing 
tapes. 

3.  Fill  out  the  letter  designations  of  the  blank  printer  magnet 
circles  of  the  Barclay  printer  shown  in  Fig.  17. 

4.  When  the  speed  of  the  Barclay  transmitter  is  such  that  forty 
current  reversals  take  place  per  second  when  running  without  tape, 
and  considering  the  length  of  the  average  letter  to  be  the  average 
of  the  characters  of  the  Barclay  code,  how  many  five-letter  words 
could  be  transmitted  per  minute  in  each  direction  with  this  printing 
system? 


CHAPTER  V 

TELEGRAPH  OFFICE  EQUIPMENT  AND  TELEGRAPH  TRAFFIC 

i.  Protective  Devices.  —  Fuses  are  used  in  telegraph 
circuits  to  protect  these  circuits  from  damage  which  might 
result  from  an  excessive  flow  of  current  through  them. 
They  are  made  of  fusible  material,  generally  of  lead  or  of 
an  alloy  of  tin  and  lead,  and  assume  the  form  of  wire  or 
strips  provided  at  each  end  with  a  copper  terminal  which 
engages  the  contacts  of  the  fuse  receptacles.  With  en- 
closed fuses  the  fusible  material  is  surrounded  by  a  finely- 
divided  non-combustible  powder  that  is  contained  in  an 
insulating  casing.  All  fuses  are  placed  at  accessible  places, 
generally  in  telegraph  offices,  so  as  to  facilitate  replacement 
in  case  of  their  melting. 

Fuses  are  rated  at  80  per  cent  of  the  greatest  current 
they  can  carry  indefinitely  without  melting.  Thus,  a 
fuse  would  carry  a  current  25  per  cent  greater  than  the 
normal  rated  current  strength.  For  telegraph  service 
fuses  of  ^-ampere  capacity  and  upward  are  used.  Line 
fuses  also  offer  protection  to  terminal  apparatus  when  the 
lines  are  crossed  with  electric  distributing  and  other  high- 
voltage  lines. 

Lightning  arresters  are  employed  at  telegraph  offices 
and  also  on  lines,  as  a  protection  against  injury  to  terminal 
apparatus  and  attendant  operators,  that  would  otherwise 
result  from  lightning  strokes  or  relieved  abnormal  induced 
charges.  These  arresters  provide  a  short  path  to  ground 

135 


136 


TELEGRAPH   ENGINEERING 


through  a  small  insulating  gap,  generally  of  air,  that  is 
readily  broken  down  and  rendered  conductive  by  such 
discharges.  The  length  of  these  gaps  is  such  that  the  oper- 
ating voltages  in  telegraph  service  cannot  initiate  arcs 
across  the  spark  gaps. 

In  practice,  satisfactory  fuses  and  lightning  arresters  for 
telegraph  circuits  assume  a  variety  of  forms,  concededly 
more  or  less  familiar.  The  type  of  protector  now  used  by 
the  Western  Union  Telegraph  Company  is  shown  in  Fig.  8. 

2.  Peg  Switch  Panels.  —  A  switching  arrangement 
adapted  for  use  at  intermediate  stations  on  simplex  lines 


Fig.  i. 

is  shown  in  Fig.  i,  and  is  called  a  peg  switch  panel  or  a  strap 
and  disc  switch  panel.  The  wall  panel  shown  is  used  where 
two-line  wires  pass  through  an  intermediate  office,  and  pro- 
vides means  for  introducing  either  set  of  receiving  instru- 
ments into  either  line,  for  cross  connecting,  for  looping 
these  lines  with  or  without  introducing  home  instruments, 
and  for  cutting  off  one  side  of  a  line. 

This  panel  consists  of  four  brass  straps  and  two  rows  of 
discs,  five  in  each  row.    The  line  terminals  are  on  the 


TELEGRAPH   OFFICE  EQUIPMENT  —  TRAFFIC         137 

upper  ends  of  the  straps,  and  the  instrument  terminals 
are  along  the  left  edge  of  the  panel.  The  latter  terminals 
are  in  line  horizontally  with  the  discs,  and  each  terminal  is 
in  electrical  connection  with  the  discs  located  in  the  same 
horizontal  row.  The  plate  g  is  placed  transversely  over 
the  straps  and  over  the  two  upper  discs,  but  is  insulated 
from  the  vertical  straps  by  a  small  air  gap,  thereby 
serving  as  the  ground  plate  of  a  lightning  arrester.  Any 
disc  may  be  connected  to  either  of  the  straps  between 
which  it  is  located  by  means  of  a  brass  plug  or  peg,  which 
fits  in  the  holes  formed  between  the  discs  and  straps.  These 
holes  are  in  five  horizontal  rows  numbered  i,  2,  3,  4  and  5, 
and  in  four  vertical  rows  lettered  a,  b,  c  and  d,  so  that  any 
one  of  the  20  holes  may  readily  be  referred  to.  Two  re- 
ceiving sets,  each  consisting  of  relay  and  key,  are  also 
shown  connected  to  the  panel  terminals.  The  insertion 
of  a  plug  in  any  of  the  four  upper  holes  grounds  the  corre- 
sponding strap. 

When  it  is  desired  to  insert  receiving  set  i  into  line  A, 
plugs  are  inserted  in  holes  02  and  d  $  (or  £3  and  d  2). 
If,  at  the  same  time,  it  be  desired  to  complete  line  B  with- 
out a  receiving  set,  plugs  are  inserted  in  holes  a  4  and  b  4 
(or  a  5  and  £5).  To  cross  connect  the  two  lines  with 
receiving  instruments  in  each  circuit,  plugs  are  placed  in 
holes  a  2  and  d  3,  and  b  4  and  c  5.  Instead,  to  cut  off  the 
western  section  of  line  A,  leaving  receiving  set  i  in  its 
other  section,  insert  plugs  in  holes  c  i,  c  2  and  d  3.  In 
order  to  loop  the  two  eastern  wires  together  with  or  with- 
out intermediate  set  i,  insert  plugs  respectively  in  holes 
b  2  and  d  3  or  in  holes  b  2  and  d  2. 

For  the  accommodation  of  additional  lines  at  inter- 
mediate or  terminal  offices,  peg  panels  having  a  corre- 


TELEGRAPH   ENGINEERING 


spondingly  greater  number  of  straps  and  discs  may  be 
used.  A  combination  of  the  peg-switch  panel  and  the 
spring-jack  device,  the  latter  shown  in  Fig.  2,  forms  a 


Fig.  2. 

widely  used  panel.  The  insertion  of  a  wedge,  as  shown, 
raises  the  shank  away  from  the  fixed  shoe  and  introduces 
into  the  line  whatever  apparatus  is  connected  with  the 
wedge  cord.  Single-  and  double-conductor  wedges  are  used 
for  various  purposes,  and  more  than  one  wedge  may  be  in- 
serted in  a  spring  jack,  thus  meeting  a  variety  of  telegraph- 
circuit  requirements. 

3.  Main  and  Loop  Switchboards.  —  In  large  telegraph 
offices  the  switching  arrangements  for  the  interconnection 
of  all  classes  of  circuits  are  located  at  switchboards.  Usu- 
ally these  switchboards  are  divided  into  two  parts:  the 
main  switchboard,  at  which  terminate  the  incoming  line 
wires,  each  wire  being  equipped  with  a  group  of  pin-jacks; 
and  the  loop  switchboard,  at  which  the  local  office  circuits 
or  loops  may  be  connected  from  one  circuit  to  another.  The 
pin- jacks  on  both  switchboards  are  so  connected  that  each 
line  or  local  circuit  is  complete  for  normal  operation. 


TELEGRAPH   OFFICE   EQUIPMENT  —  TRAFFIC         139 


Changes  in  these  normal  conditions  are  effected  by  single 

or  double  flexible  conductors  or  patching  cords  having  plug 

terminals  which  fit  into  the  jacks.     Fig.  3  shows  the  type 

of  pin- jacks  and  plugs 

now  extensively  used  on 

telegraph  and  telephone 

switchboards. 

Main  Switchboards.  — 
All  line  wires  terminate 
at  the  main  switchboard 
which  is  equipped  with  Fi«-  3. 

properly  connected  jacks  for  the  establishment   of   any 
desired  connections  with  these  wires. 

A  main  switchboard  comprises  a  variety  of  circuits.    A 


.  BUSY  TEST  KNOBS 


TO  LOOPP 
VIA  DI8TRIB 


40  -  3  LOOP  SIMPLEX  MORSE  WIRE 


Fig.  4- 


typical  panel  of  the  Western  Union  main  switchboard 
for  terminal  offices  contains  nine  types  of  circuits,  five  of 
which  are  shown  in  Fig.  4,  the  number  of  circuits  of  each 


140 


TELEGRAPH   ENGINEERING 


type    being    indicated.     The    remaining    four    types    are 
shown  as  circuits  A,  D,  E  and  F  in  Fig.  6  in  connection 


RESISTANCE 

LAMP3 

CABLE  FROM  LAMPS 
TO  LOCAL  BATTERY  FUSES 

a 


REAR  VIEW  OF 
CABLING  FOR 
FLOOR  DUCTS 


SECTION 
Fig.  5- 


FRONT  VIEW 


with  the  loop  switchboard,  twenty  A,  four  D,  ten  E  and 
twenty  F  circuits  being  employed.  Circuits  for  combined 
telegraphy  and  telephony  are  also  provided  where  necessary. 


TELEGRAPH  OFFICE  EQUIPMENT  —  TRAFFIC         141 


RESISTANCE  LAMP  (3  -  12   OHMS  PER  VOLT) 

~ 


20  •  TWO-WIRE  TRUNKS  (FROM  ONE 
'    END  OF  BOARD  TO  OTHER ) 


fr-^"- 

*-^~l  SOUNDE 


10  -  DUPLEX  OR  QUAD.  SETS    AND  REGULARLY 
ASSIGNED  LOOPS 


RESISTANCE 
LAMPS 


80-    DUPLEX   LOOPS  WITHOUT  REGULAR   ASSIGNMENT 


POLE  CHANGE 


TO  MAIN  SWITCH-          ) 
BOARD   JACKS  OR  >- 

REPEATERS  VIA  I 

DISTRIBUTING   FRAME  )~ 


(D 


'II 


64  -  TWO  WIRE  TRUNKS  TO  MAIN  SWITCH  B'D. 
20  -  HALF-REPEATER  LOOPS   <2  FOR  EACH  ) 
20  -  FULL-REPEATER  LOOPS  (  2  FOR  EACH  ) 
24-  DOUBLE  LOOP  REPEATERS  (3  FOR  EACH) 


16 -DUPLEX  OR  HALF-QUAD.  REPEATER  LOOPS. 


8-TE8TING8ET8 


Fig.  6. 


142  TELEGRAPH  ENGINEERING 

Referring  to  Fig.  4;  circuit  B  is  used  for  simplex  service 
which  may  require  three  loops  or  sets  each,  the  loops  being 
included  by  inserting  the  plugs  of  patching  cords  in  jacks 
7-8,  9-10  and  11-12;  circuit  C  is  used  on  multi-section 
switchboards  for  extending  loops  and  other  circuits  from 
one  section  to  another;  circuit  G  is  used  in  cases  of  loop 
failures  and  circuit  H  is  used  for  testing  purposes  where 
it  is  required  to  ground  a  line.  For  duplex  or  quadruplex 
circuits  it  is  only  necessary  to  connect  the  line  through 
three  jacks  to  the  corresponding  set  via  the  loop  switch- 
board and  distributing  frame,  as  indicated  by  circuit  /. 

The  design  of  this  switchboard  is  shown  in  Fig.  5,  the 
jacks  bearing  numbers  corresponding  to  those  in  Fig.  4. 

Loop  Switchboards.  —  A  loop  switchboard  is  generally 
installed  at  large  telegraph  offices  to  provide  facilities  for 
conveniently  changing  local  circuit  connections  of  duplex 
and  quadruplex  sets  from  one  operating  table  to  another 
at  the  main  office  or  for  distributing  these  connections  to 
subscribers  or  branch  offices,  so  as  to  take  care  of  varying 
traffic  requirements.  The  terminals  of  such  local  circuits 
extend  to  pin  jacks  on  the  loop  switchboard,  the  board  cir- 
cuits being  so  arranged  that  the  local  apparatus  regularly 
assigned  to  the  same  circuit  is  normally  conriected  thereto, 
changes  in  these  connections  being  made  with  flexible 
patching  cords. 

A  loop  switchboard  includes  a  variety  of  circuits.  A 
typical  panel  of  the  Western  Union  one-section  loop  switch- 
board comprises  the  eleven  types  of  circuits  shown  in 
Fig.  6,  the  number  of  circuits  of  each  type  being  indicated. 

Circuit  A  is  used  in  the  testing  of  simplex  circuits;  cir- 
cuit B  is  used  in  testing,  or  in  case  of  failure  of  the  resist- 
ances or  contacts  of  an  office  loop,  it  replaces  the  lower 


TELEGRAPH   OFFICE   EQUIPMENT  —  TRAFFIC         143 

jack  of  circuit  G;  circuits  C  and  D  enable  simplex  apparatus, 
loops,  repeaters,  etc.,  to  be  readily  joined  in  series,  the 
former  including  a  current  source;  circuit  E  permits  of  the 
interconnection  of  apparatus  terminating  at  remote  por- 
tions of  the  board  by  means  of  two  short  patching  cords 
instead  of  one  long  one;  the  jacks  of  circuit  F  connect 
with  receiving  sets,  repeaters,  half -repeaters,  etc.,  or  extend 
to  jacks  on  the  main  switchboard;  circuits  G  and  H  con- 
nect the  apparatus  of  a  duplex  or  quadruplex  set  for 
normal  operation,  the  latter  circuit  being  used  where  an 
outside  loop  is  regularly  assigned  to  the  set;  circuit  /  is 
used  for  branch  office  loops  that  are  not  regularly  assigned 
to  any  particular  duplex  set,  and  may  replace  those  nor- 
mally assigned  in  circuits  G  and  H;  circuit  /  normally 
joins  the  two  duplex  or  half -quadruplex  sets  that  constitute 
the  duplex  repeater;  circuit  K  serves  as  a  testing  set  for 
making  any  desired  tests  on  duplex  or  quadruplex  sets. 

4.  Distributing  Frames.  —  Before  telegraph  aerial  or 
underground  lines  reach  the  main  switchboard  at  an  office 
they  pass  through  a  distributing  frame  generally  placed 
in  back  of  the  switchboard.  Office  cables  extend  from  this 
frame  to  the  main  and  loop  switchboards  and  to  the  instru- 
ment tables  on-  which  repeater,  duplex  and  quadruplex 
apparatus  are  located.  Fig.  7  shows  three  units  of  a 
Western  Union  distributing  frame.  The  right  or  "  hori- 
zontal" side  has  8  horizontal  strips  which  carry  terminal 
blocks  for  connection,  say,  to  office  apparatus,  while  the 
left  or  " vertical"  side  has  3  vertical  strips  which  may 
carry  similar  terminal  blocks  or  office  protectors  and  con- 
nect with  the  incoming  line  cables.  Each  horizontal  seg- 
ment accommodates  20  terminal  clips  for  an  equal  number 


144 


TELEGRAPH   ENGINEERING 


Fig.  7. 


TELEGRAPH  OFFICE   EQUIPMENT  —  TRAFFIC         145 


of  wires  and  each  vertical  strip  accommodates  100  pro- 
tectors. These  connections  to  terminal  clips  and  pro- 
tectors are  permanent.  Any  desired  connection  may  be 
made  between  the  different  pieces  of  apparatus  in  the 
office,  or  between  such  apparatus  and  entering  lines,  by 
cross-connecting  or  " bridle"  wires  at  the  distributing 
frame.  Switchboard  rearrangements  or  changes  in  traffic 
requirements  are,  therefore,  readily  met  by  shifting  the 
bridle  wires  without  altering  the  apparatus  and  line  wiring 
to  the  distributing  frame. 

The  type  of  protector  used  comprises  a  one-half  ampere 


^AMPERE  FUSE 


RELAXED  SPRING  INDICATES 
BLOWN  FU6E 


| |  LIGHTNING  ARRESTER 


GROUND  PLATE 


Fig.  8. 

indicating  fuse  and  a  lightning  arrester  formed  by  two 
carbon  blocks  separated  by  a  thin  strip  of  mica,  and  is 
shown  in  Fig.  8. 

5.  Instrument  Tables.  —  Telegraph  apparatus  at  large 
telegraph  offices  is  arranged  in  a  very  compact  form  on 
instrument  tables.  One  general  form  of  instrument  table 
construction  is  shown  in  Fig.  9,  which  shows  that  portion 
of  one  side  of  a  long  table  occupied  by  the  apparatus  of 
one  quadruplex  set.  A  duplex  set  requires  about  13  inches 
and  a  duplex  repeater  set  about  33  inches  of  table  length. 

The  location  of  the  apparatus  of  a  Western  Union 
quadruplex  set  on  this  table  is  generally  as  indicated  in 


146 


TELEGRAPH  ENGINEERING 


the  figure,  the  upper  shelf  being  reserved  for  signalling 
purposes.  The  unit-section  instrument  tables  used  by  the 
Postal  Telegraph  Cable  Company  are  constructed  of  angle 
and  sheet  iron  with  apparatus  located  on  four  narrow  tiers, 
each  unit  accommodating  two  quadruplex  sets,  or  four 
duplex  sets,  or  four  repeater  sets. 

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RELAY  S  ' 


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Attendants  constantly  oversee  the  operation  of  such 
duplex,  quadruplex  and  repeating  apparatus,  each  attend- 
ant having  supervision  of  a  certain  number  of  sets. 

6.  Power  Switchboards.  —  A  switchboard  for  a  tele- 
graph power  plant  should  comprise  the  necessary  switching 
facilities,  measuring  and  regulating  devices  for  the  placing 
of  the  desired  potentials  of  correct  polarity  on  the  terminals 


TELEGRAPH  OFFICE   EQUIPMENT  —  TRAFFIC         147 

of  the  distributing  panel  from  which  conductors  lead  to  the 
main  switchboard.  As  most  telegraph  power  plants  con- 
sist of  motor-generator  units,  which  alter  the  voltage  of 
the  available  commercial  current  supply  to  values  suitable 
for  telegraphic  purposes,  switchboards  for  such  plants 
should  also  include  motor-starting  switches  and  rheostats. 
To  maintain  continuity  of  service  in  case  of  shut-down  of 
the  commercial  current  supply,  arrangements  are  made  if 
possible,  for  break-down  connection  with  another  source, 
or,  if  the  available  current  sources  are  not  dependable, 
a  storage  battery  or,  where  practicable,  a  steam,  gas  or 
oil  engine  and  generator,  is  installed. 

The  appearance  of  a  typical  power  switchboard  now  used 
by  the  Western  Union  Telegraph  Company  for  a  motor- 
generator  plant  is  shown  in  Fig.  10,  scale  gV-  The  board  is 
mounted  directly  over  the  machines,  each  panel  controlling 
the  motor-generators  below  it.  The  left-hand  panel  con- 
trols three  machines,  one  generator  having  its  positive  ter- 
minal permanently  grounded,  another  its  negative  terminal 
grounded,  and  the  middle  generator  serves  as  a  spare  unit 
which  may  replace  either  of  the  others  by  shifting  the  re- 
versing switch.  The  smaller  switchboard  panel  is  intended 
for  two  machines,  one  delivering  current  to  the  local  cir- 
cuits and  the  other  a  spare  unit.  All  generator  and  motor- 
starting  switches  and  the  voltmeters  are  provided  with 
enclosed  fuses  on  the  face  of  the  board. 

The  connections  of  this  power  board  for  motor-generators 
with  direct-current  motors  are  shown  in  Fig.  n.  Three 
1 60- volt  and  two  2  6- volt  motor-driven  .  generators  are 
shown,  the  outer  i6o-volt  machines  and  the  left-hand 
26-volt  machine  being  in  service.  When  the  middle 
i6o-volt  generator  is  to  replace  its  left  neighbor,  it  is 


148 


TELEGRAPH  ENGINEERING 


TELEGRAPH   OFFICE    EQUIPMENT  —  TRAFFIC         149 


150  TELEGRAPH  ENGINEERING 

started  and  brought  up  to  proper  voltage  by  means  of  its 
field-regulating  rheostat  RR  and  placed  in  parallel  with 
its  neighbor  by  throwing  switch  E  to  the  left  and  closing 
switch  B.  Thereafter  switches  A  and  then  F  are  opened. 
In  the  figure  V  and  A  indicate  voltmeters  and  ammeters 
respectively,  /  indicates  fuses  and  SR  represents  motor- 
starting  rheostats  with  no-voltage  release,  the  terminals 
marked  M,  A  and  F  connecting  with  the  service  main, 
motor  armature  and  motor  field  respectively.  The  gener- 
ator leads  go  to  a  distributing  panel  which  provides  con- 
venient means  for  distributing  the  proper  current  to  the 
various  classes  of  circuits.  This  panel  also  includes  the 
main  service  switch  and  instruments. 

Switchboards  for  motor-generators,  having  alternating- 
current  single-phase,  two-phase  or  three-phase  motors, 
differ  slightly  from  the  board  described  in  that  different 
starting  devices  and  motor  switches  are  employed. 

TRAFFIC 

7.  Types  of  Messages.  —  Messages  for  telegraphic 
transmission  may  be  written  in  plain  language,  be  expressed 
in  code  words,  or  be  couched  in  cipher.  Code  words  are 
actual  or  artificial  pronounceable  words  having  not  more 
than  10  letters.  The  object  of  employing  code  words  is 
the  saving  of  telegraph  tolls,  inasmuch  as  a  single  word  is 
given  a  meaning  expressible  in  plain  language  only  by 
several  words  or  even  a  sentence.  A  few  code  words  with 
their  interpretation  according  to  the  Western  Union 
Travelers'  code  are  given  below: 

ALLAH  Arrived  all  right,  address  letters  to  care  of 

BALMY  Are  very  busy.    Please  return  soon  as  possible. 

BRING  There  is  no  occasion  for  alarm. 

COVER  Can  you  send  me  letter  of  introduction  to ? 


TELEGRAPH  OFFICE   EQUIPMENT  —  TRAFFIC          151 


ENTER      Arrangements  are  progressing  satisfactorily. 

LUNAR      I  (or )  do  not  wish  to  take  responsibility  for  deciding. 

You  (or  )  know  all  the  circumstances  and  must 

decide  what  shall  be  done. 
PEGGY      Market   very   strong.     Prices   have    advanced   since   last 

advice. 

PUNCH      Please  accept  my  heartiest  congratulations. 
SPIKE        Have  sent  telegraphic  money  order  as  requested. 
SCORN      We  wish  you  all  a  Happy  New  Year. 

Cipher  messages  are  used  solely  for  secrecy.  Such 
messages  consist  of  unpronounceable  groups  of  letters  or 
of  groups  of  figures,  or  both.  They  can  be  read  only  by 
the  sender  and  recipient,  in  accordance  with  some  pre- 
arranged scheme.  Considerable  time  is  necessary  for 
couching  and  deciphering  such  cipher  messages.  As  an 
illustration,  the  Confederate  cipher  used  during  the  Civil 
War  will  be  cited,  the  keywords  employed  by  the  Confed- 
erates being  "Complete  Victory,"  ^Manchester  Bluff" 
and  later  "  Interest. "  The  cipher  is  made  up  by  giving 
numbers  to  the  letters  of  the  alphabet  as  below: 

abcdef     ghi     j    k   1     mnopqrstuvwxyz 
I    2    3    4    5    6    7    8    9    10  n  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26 
27  28  29  3°  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52 

To  write  a  cipher  message  add  the  respective  numbers 
corresponding  to  the  letters  of  the  keyword  and  of  the 
message  (letter  for  letter,  repeating  the  keyword  if  neces- 
sary), subtract  the  index  number  i,  and  the  corresponding 
letters  will  yield  the  cipher  message.  Thus  to  write 
" Reach  Richmond  to-day,"  using  the  keyword  " Interest," 
proceed  as  below: 

R  I  CHMOND 
18  9  3  8  13  15  14  4 
E  S  T  I  N  T  E  R 
5  19  20  9  14  20  5  18 


REACH 
185    i    3    8 

INTER 

9    14  20  5    18 

Sum  minus  one  26  18  20  7    25 

Z   R  T  G  Y 


22   2?   22   l6   26  34   18   21 

VAVPZHRU 


TODAY  (message) 
20  15  4    i    25 
E  S   T  I    N  (keyword) 
5    19  20  9    14 

24  33  23  9    38 

X  G  W  I    L   (cipher) 


The  last  line  is  the  appropriate  cipher  message. 


152  TELEGRAPH  ENGINEERING 

To  decipher  a  message  according  to  this  cipher,  subtract 
numbers  corresponding  to  keyword  from  number  corre- 
sponding to  cipher  (letter  for  letter),  add  the  index  num- 
ber i,  and  the  corresponding  letters  will  yield  the  message. 
By  varying  this  scheme  and  using  different  keywords,  an 
infinite  variety  of  cipher  codes  may  be  developed.  The 
characters  of  cipher  words  are  transmitted  with  double 
spacing  as  a  safeguard  for  avoiding  errors. 

8.  Classes  of  Service  and  Tariffs.  —  Several  classes  of 
telegraph  service  are  rendered  by  the  large  telegraph  com- 
panies. The  overland  services  offered  by  the  Postal  and 
Western  Union  Companies  are:  telegrams  and  night  letters; 
the  latter  company  also  offers  day  letters. 

Present  rates  (1914)  for  commercial  telegrams  from  New 
York  City  to  the  capitals  of  the  states  and  territories  in 
the  United  States  and  of  some  of  the  provinces  in  the 
Dominion  of  Canada,  are  given  in  the  table  on  the  follow- 
ing page,  which  includes  also  the  rates  to  Mexico  City  and 
Dawson  City,  Yukon.  Day  rates  apply  to  messages  in- 
tended for  immediate  delivery  whereas  night  rates  apply  to 
telegrams  for  delivery  the  following  morning.  The  number 
before  the  dash  is  the  rate  in  cents  for  telegrams  of  10  words 
or  less  (address  and  one  signature  free),  and  the  number 
following  the  dash  is  the  charge  for  each  additional  word. 

Night  letters  containing  50  words  (or  less)  may  be  sent 
at  the  lo-word  day  message  rate,  one-fifth  of  this  rate  being 
charged  for  each  additional  group  of  10  words;  and  day 
letters  of  50  words  (or  less)  may  be  sent  at  ij  times  the 
night  letter  rate.  Day  letters  are  forwarded  as  promptly 
as  the  facilities  of  the  company  permit  only  in  subordination 
to  the  full-paid  telegrams,  and  night  letters  are  trans- 


TELEGRAPH  OFFICE   EQUIPMENT  —  TRAFFIC         153 


RE 

ites 

Citv 

Ra 

tes 

Day 

Night 

Day 

Night 

60-4 

5O-3 

Carson  City,  Nev. 

100-7 

100-7 

Juneau,  Alaska  
Phoenix    Ariz. 

260-23 
100-7 

260-23 
100-7 

Fredericton,  N.  B  
Concord,  N.  H. 

50-3 
35-2 

40-3 
25-1 

Little  Rock  Ark 

60-4 

50-3 

Trenton,  N.  J. 

25-2 

25-1 

Victoria,  Brit.  Col  

100-7 
100-7 

100-7 
100-7 

Santa  Fe*.  N.  Mex  
Albany,  N.  Y. 

75-5 
25-2 

60-4 
25-1 

Denver,  Col  
Hartford   Conn. 

75-5 
25-2 

60-4 
25-1 

Raleigh,  N.  C  
Bismarck,  N.  Dak. 

50-3 
75-5 

40-3 
60-4 

Dover,  Del  
Washington,  D.  C. 

30-2 
30-2 

25-1 
25-1 

Halifax,  N.  S  
Columbus,  Ohio 

50-3 
40-3 

40-3    . 
•50-2 

(National  capitol) 
Tallahassee,  Fla. 

60-4 

50-3 

Oklahoma  City,  Okla.  .  . 
Ottawa,  Ont.  . 

75-5 
50-3 

60-4 
4O-3 

Atlanta,  Ga  
Boise,  Id  
Springfield  111. 

60-4 
100-7 
50-3 

50-3 
100-7 
40-3 

(Capitol  of  Dominion) 
Toronto,  Ont  
Salem,  Ore. 

50-3 

100-7 

40-3 
100-7 

Indianapolis,  Ind  
Des  Moines,  la. 

50-3 
60-4 

40-3 
50-3 

Harrisburg,  Pa  
Charlottetown,  P.  E.  I.. 

30-2 
75-5 

25-1 
65-5 

Topeka,  Kan  
Frankfort,  Ky. 

60-4 
50-3 

50-3 
40-3 

?uebec,  Quebec  
rovidence,  R.  I. 

50-3 
30-2 

40-3 
25-1 

Baton  Rouge,  La  
Augusta,  Me. 

60-4 
40-3 

50-3 
30-2 

Columbia,  S.  C  
Pierre,  S.  Dak.. 

60-4 
75-5 

50-3 
60-4 

Winnipeg  Manitoba 

75-5 

60-4 

Nashville  Tenn. 

50-3 

40-3 

Annapolis,  Md  
Boston,  Mass. 

30-2 
30-2 

25-1 
25-1 

Austin,  Tex  
Salt  Lake  City,  Utah. 

75-5 
75-5 

60-4 
60-4 

Mexico  City,  Mexico  
Lansing,  Mich. 

175-12 
50-3 

175-12 
40-3 

Montpelier,  Vt  
Richmond,  Va. 

35-2 
40-3 

25-1 
30-2 

St.  Paul   Minn 

60-4 

50-3 

Olympia   Wash 

100-7 

100-7 

Jackson,  Miss  
Jefferson  City,  Mo. 

60-4 
60-4 

50-3 
50-3 

Charlestown,  W.  Va  
Madison,  Wis. 

40-3 
60-4 

30-2 
50-3 

Helena,  Mont  
Lincoln,  Neb  -.  .   .  . 

75-5 
60-4 

60-4 
50-3 

Cheyenne,  Wyo  
Dawson  City,  Yukon.  .  . 

75-5 
425-29 

60-4 
425-29 

mitted  sometime  during  the  night  at  the  convenience  of 
the  company  and  are  delivered  the  following  morning. 
Such  deferred  service  is  offered  at  attractive  rates  in  order 
to  keep  the  equipment  effectively  busy  at  all  hours,  or  in 
other  words,  to  keep  up  the  load  factor  of  the  equipment. 

Day  and. night  letters  must  be  written  in  plain  English 
and  must  not  contain  code  words.  The  letters  BLUE, 
NL  or  NITE  are  prefixed  to  a  message  and  transmitted 
to  inform  the  receiving  operator  as  to  the  class  of  service 
desired,  whether  day  letters,  night  letters  or  night-rate 
telegrams  respectively.  The  indication  DH  (representing 
dead  head)  is  used  on  unpaid  messages  for  company  matters, 
etc.  When  a  group  of  messages  of  one  class  is  transmitted, 


154 


TELEGRAPH  ENGINEERING 


a  single  indication  on  the  first  message  of  a  group  suffices 
for  successive  messages  until  a  different  indication  is  re- 
ceived. 

A  message  blank  bearing  a  message  for  transmission 
should  contain  the  following  information: 


ITEM  No.  ITEM 

1  Originating  city 

2  Date 

3  Addressee  (name  and  address) 

4  Message 

5  Signature 

6  Indication  as  to  class  of  service 

(Different  blanks  are  used  for  the 
various  classes.) 

7  Telegraph  clerk's  number 

8  Time  of  filing 

9  Check  of  number  of  words 

10  Wire  number 

11  Office  call  letter  at  destination 

12  Sending  operator's  sign 

13  Time  of  transmission 

14  Receiving  operator's  sign 


BY  WHOM  WRITTEN 


Sender  or  telegraph 
clerk. 


Telegraph  clerk. 


Sending  operator. 


The  first  six,  the  ninth,  tenth,  thirteenth  and  fourteenth 
items  as  well  as  the  call-letter  of  the  originating  office  are 
transmitted  and  appear  upon  the  received  message  blank 
that  is  delivered  to  the  addressee.  If  a  reply  is  to  be  pre- 
paid the  letters  RP  followed  by  the  number  of  words  pre- 
paid are  transmitted  and  also  appear  upon  sending  and 
receiving  message  blanks. 

9.  Handling  of  Traffic.  —  The  methods  employed  in 
handling  commercial  telegraphic  traffic  depends  largely 
upon  the  volume  of  incoming  and  outgoing  traffic.  In  a 
large  center  the  handling  of  this  traffic  at  the  main  office 
must  be  fully  systematized  in  order  to  facilitate  prompt 


TELEGRAPH  OFFICE  EQUIPMENT  —  TRAFFIC         155 

transmission  and  delivery  of  messages.  Somewhat  differ- 
ent methods  of  handling  traffic  are  naturally  employed  at 
different  places;  that  used  in  a  large  city  will  here  be  out- 
lined. 

The  telegraphic  stations  of  a  city  for  the  reception  and 
transmission  of  messages  comprise  a  main  office  and  many 
branch  offices  distributed  throughout  the  city.  The  Wes- 
tern Union  Telegraph  Company  has  about  200  branch 
offices  in  New  York  City.  Messages  for  transmission  may 
reach  these  branch  offices  either  by  submission  in  person 
or  by  representative,  or  may  be  collected  by  messenger 
upon  call,  no  charge  being  made  for  this  service.  Messages 
may  also  be  telephoned  from  telephone  subscribers'  stations 
to  the  main  office  by  requesting  the  telephone  operator 
for  "Western  Union"  or  for  "Postal,"  and  upon  connec- 
tion, dictating  the  message  to  the  answering  telegraph 
clerk.  The  tolls  for  a  message  so  sent  will  either  be  col- 
lected upon  delivery  or  will  be  charged  to  the  sender  on 
his  telephone  bill.  Messages  received  at  branch  offices 
are  sent  to  the  main  office  in  two  ways :  the  blanks  may  be 
carried  by  pneumatic  tube  carriers  from  those  offices  that 
are  connected  with  the  main  office  by  such  tubes,  or  else 
the  message  is  telegraphed  to  the  main  office. 

The  messages  arriving  at  the  main  office  for  telegraphic 
transmission  are  sorted  at  a  central  distributing  place  or 
routing  room  and  are  distributed  by  mechanical  carriers 
to  division  stations,  each  division  being  a  portion  of  the 
operating  floor  seating  operators  who  transmit  on  lines 
terminating  in  some  geographical  division  of  the  country. 
Check  boys  or  girls  carry  the  message  blanks  from  the 
division  stations  to  the  proper  operators.  After  the  oper- 
ators have  transmitted  a  message,  they  indorse  the  blank 


156  TELEGRAPH    ENGINEERING 

(by  inscribing  items  10-14  of  the  scheme  given  in  foregoing 
section)  and  place  it  in  a  message  clip.  Check  boys  pass 
up  and  down  the  aisles  and  remove  the  blanks  from  the 
clips  and  take  them  to  the  division  stations  from  whence 
they  are  carried  mechanically  to  a  searching  room.  Here 
the  blanks  are  examined  as  to  the  indorsement  and  are 
filed  away  and  preserved  for  a  reasonable  length  of  time. 

Incoming  messages  are  typewritten  upon  suitable  blanks 
by  the  receiving  operators  or  are  automatically  printed  by 
the  printing  telegraphs.  These  incoming  messages  are 
carried  by  check  boys  and  mechanical  carriers  to  the 
routing  room,  where  they  are  sorted.  Such  messages  re- 
quiring retransmission  are  carried  to  the  proper  sending 
operator  in  the  same  way  as  originating  messages.  The 
remaining  messages  are  for  local  distribution  within  the 
city  confines.  These  city  messages  are  sorted  and  may 
be  telephoned  directly  to  the  addressee  if  he  be  a  telephone 
subscriber,  or  else  sent  to  his  nearest  branch  office  either 
by  pneumatic  tube  or  by  wire,  and  from  there  delivered 
by  messenger  to  the  addressee. 

The  traffic  manager  at  a  large  telegraph  office  is  kept 
constantly  informed  regarding  the  amount  of  traffic  over 
the  various  interurban  and  important  lines,  so  that  if 
necessary  he  may  alter  the  customary  routing  of  messages 
in  order  that  telegraphic  business  at  all  centers  may  be 
adequately  disposed  of  with  the  available  existing  facilities. 
Thus,  if  an  unusual  amount  of  traffic  has  accumulated  at 
Philadelphia  for  transmission  to  Chicago  via  New  York, 
and  if  the  traffic  from  Philadelphia  to  Boston,  and  from 
Boston  to  Chicago  is  light,  the  traffic  manager  would 
direct  the  operators  at  Philadelphia  to  send  some  of  the 
messages  to  Chicago  via  Boston.  In  the  event  of  severe 


TELEGRAPH  OFFICE  EQUIPMENT  —  TRAFFIC          157 

storms  felling  pole-lines  between  important  centers,  the 
traffic  manager  endeavors  to  re-establish  service  between 
these  points  over  another  route  even  if  very  circuitous. 

Records  of  the  amounts  of  traffic  accommodated  on  the 
various  line  circuits  are  kept  for  the  information  of  tele- 
graph engineers  who  determine  the  necessity  for  additional 
lines  and  equipment  or  suggest  rearrangements  of  existing 
facilities  for  improving  the  service. 

10.  The  Telegraph  in  Railway  Operation. — The  hand- 
ling of  steam  trains  in  accordance  with  telegraphic  orders 
began  in  1851,  and  since  that  time  has  been  rapidly  ex- 
tended to  all  railroad  systems.  Since  1907  the  telephone 
'  is  also  used  in  train  dispatching  and  in  the  directing  of  train 
movements;  at  present,  about  70,000  miles  of  railroad  in 
this  country  are  telephonically  handled. 

A  large  majority  of  all  telegraph  offices  in  the  United 
States  are  located  in  railway  stations,  and  large  amounts 
of  commercial  and  especially  railway  telegraph  traffic  are 
handled  through  them.  Railway  telegraph  traffic  may 
deal  with  inter-departmental  business  or  with  train  move- 
ments, the  latter  traffic  being  usually  urgent  and  requiring 
immediate  attention.  Such  traffic  on  a  railroad  division 
includes  the  progress  of  passenger  and  freight  trains, 
attendance  to  emeVgencies  as  they  arise,  information  on 
the  location  of  rolling  stock,  messages  concerning  ship- 
ments, and  so  on. 

The  use  of  the  telegraph  for  issuing  and  receiving  such 
information  generally  requires  two  local  single-wire  circuits 
linking  the  principal  office  of  the  division  with  its  various 
local  offices.  One  of  these  circuits,  termed  the  train  wire, 
is  used  by  the  train  dispatcher,  and  the  other,  termed  the 


158 


TELEGRAPH  ENGINEERING 


message  wire,  is  used  for  transmission  of  commercial  and 
railway  telegrams.  On  unimportant  branch  roads  both  ser- 
vices are  sometimes  handled  over  a  single  circuit,  whereas 
on  long  or  busy  railway  divisions  the  more  important 
offices  may  be  connected  to  a  special  circuit  to  relieve  con- 
gestion of  traffic  on  the  other  circuits.  Between  the 
principal  division  offices  of  a  system  and  the  general  offices 
or  administrative  center  of  the  railroad  are  a  series  of 
circuits,  which  may  be  operated  simplex,  duplex  or  quad- 
ruplex,  with  or  without  repeaters,  as  the  traffic  or  length 
of  the  circuit  may  warrant.  Thus,  an  idea  of  the  extent 
of  the  telegraph  circuits  of  the  Northern  Pacific  system 
(which  operates  over  6000  miles  of  main-line  track)  may  be 
gained  from  the  following  list  of  principal  circuits  now 
operated  out  of  the  St.  Paul,  Minn.,  general  office.  This 
list,  given  by  M.  H.  Clapp,  does  not  include  some  local 
circuits  operating  out  of  St.  Paul  to  points  in  the  direct 
vicinity  of  the  Twin  Cities.  There  are  four  repeating 
stations  on  the  St.  Paul-Tacoma  line,  at  which  traffic  is 
also  relayed  to  different  offices  to  which  direct  wires  are 
not  provided. 


Circuit  from  St.  Paul  to 

Circuit 
operated 

Distance 
in  miles 

Tacorna  Wash                                                     .       ... 

Quadruplex 

1900 

1250 

1650 

Helena,  Mont  

1130 

Billings  and  Livingston,  Mont.        

1008 

Dickinson  N.  D.  and  Glendive,  Mont  .... 

667 

Fargo  N   D    and  Dilworth  Minn. 

252 

Duluth  Minn 

Duplex 

152 

Winnipeg,  Man.  —  Local  32  offices  

Simplex 

483 

Fargo,  N.  D.  —  Local  41  offices  

252 

Duluth  Minn.  —  Local  40  offices  .          

«• 

152 

St  Paul  Division.  —  Local  30  offices 

•« 

170 

TELEGRAPH  OFFICE   EQUIPMENT  —  TRAFFIC         159 


ii.  Telegraph  Statistics.  —  The  United  States  censuses 
of  electrical  industries  show  the  following  statistics  of  the 
domestic  telegraph  industry  in  the  years  1880,  1902,  1907 
and  1912: 

COMMERCIAL  LAND  AND  OCEAN  TELEGRAPH  SYSTEMS 


1880 

1902 

1907 

1912 

Number  of  companies  or  sys- 
tems 

77 

25 

25 

27 

Nautical  miles  of  ocean  cable.  . 
Miles  of  single  wire  owned  and 
leased  
Number  of  messages  
Number  of  telegraph  offices  
Dollars  total  income 

(a) 

291,213 
31,703,181  (d) 
12,510 
16,696,623 

16,677 

1,318,350  (b) 
91,655.287 
27,377 
40,930,038 

46,301 

1,577,961 
103,794.076 
29,056 
51  583  868 

67,676 

1,814,196  (c) 
109,377,698 
30.864 
64  762  843 

Average  number  of  employees(e) 
Employees  salaries  and  wages 
(dollars)  (g)  

14,928 
4,886,128 

27,627 
15,039,673 

28,034  (/) 
17,808,249 

37,295 
24,964,994 

(a)  Not  separately  reported. 

(b)  Includes  miles  of  wire  operated  by  W.  U.  Tel.  Co.  outside  of  the  United  States. 

(c)  Exclusive  of  314,329  miles  of  wire  wholly  owned  and  operated  by  railway  companies 
for  their  own  business. 

(d)  For  54  companies  out  of  77. 

(e)  Does  not  include  railway  operators  also  doing  work  for  telegraph  companies. 
(/)  For  23  companies  out  of  25. 

(g)  Two  companies  in  1907  and  one  in  1902  did  not  separate  salaries  and  wages  from  oper- 
ation expense.  The  wages  of  persons  enumerated  above  spending  a  part  of  their  time 
in  telegraph  service  are  those  received  for  telegraphic  service  only. 

The  large  decrease  in  the  number  of  separate  companies 
from  1880  to  1902  was  due  to  numerous  consolidations  of 
formerly  competing  companies.  Far  more  than  one-half 
of  the  number  of  telegraph  offices  tabulated  are  located 
in  railway  stations,  and  these  offices  are  not  used  exclu- 
sively for  the  transmission  of  messages  for  the  general  public. 

The  extent  to  which  the  telegraph  industry  is  controlled 
by  a  few  companies  is  indicated  by  the  fact  that  the  six 
largest  companies  reported  99  and  97.7  per  cent  of  the  total 
tabulated  income  in  the  years  1902  and  1907,  respectively. 


i6o 


TELEGRAPH   ENGINEERING 


The  1907  census  also  shows  that  625  railway  companies 
in  the  United  States,  operating  225,059  miles  of  single  track, 
owned  383,833  and  leased  423,991  miles  of  telegraph  wire, 
and  sent  258,589,333  telegraph  messages  for  railroad  busi- 
ness during  the  year. 

Comparative  telegraphic  statistics  of  various  countries 
selected  from  Senate  Document  No.  399,  dated  1914,  for 
the  year  1910  (except  where  otherwise  stated)  are  tabu- 
lated below: 

TELEGRAPH  STATISTICS  OF  DIFFERENT  NATIONS 


Country 

Population 

Annual 
telegrams 
per  capita 

Average 
receipt  per 
domestic 
telegram 
in  cents 

Telegraph 
offices 

Miles  of 
telegraph 
wire 

Per  10,000  of  population 

Austria  
Belgium  

28,571,934 
7,074,91° 
2,585,660 
38,961,945 
63,886,000 
41,976,827 
20,886,487 
32,475,253 
49.732,952 
246,455 
5,591.701 
1,062,792 
2,240,032 
152,009,300 
5,294,885 
3,315,443 

95.410,503 

0.73 
1.25 
1.  31 
1.65 
0.92 
2.18 
0.59 
0.55 
0.60 
0.84 
1.19 
8.09 
1.48 
0.24 
0.80 
1.75 

1.09 

22.4 
14.2 

14.0 

12.  1 

18.0 
17.2 
25.1 
19-3  (a) 
12.3 
9-0 
15-0 
15-7 
I3.4(a) 
42.0 
15  3 
17.2 

45.0 

1.58 
2.31 
2.17 

5-21 

7.06 
3-33 

2.20 
2.36 

0.86 
13.16 
2.49 
18.51 
7.08 
0.55 
5-39 
7.13 

3-42 

50 
36 
34 
108 
175 
135 
42 
38 

20 
29 
40 

357 
142 
•28 
37 
48 

190 

Denmark 

France  

Germany  
Great  Britain  
Hungary 

Italy 

Japan  
Luxemburg  (1905)  .  .  . 
Netherlands  . 

New  Zealand 

Norway  

Russia  
Sweden 

Switzerland  

United  States  (1912) 
(b)  

(a)  Minimum  message  rate. 

(b)  Statistics  computed  from  preliminary  report  on  Land  Telegraph  Stations:    1912, 
issued  Feb.,  1914. 

It  will  be  observed  that  of  the  countries  tabulated,  the 
average  cost  per  telegram  is  least  in  Luxemburg  and  most 
in  the  United  States,  and  that  the  yearly  telegrams  per 
individual  is  most  in  New  Zealand  and  least  in  Russia. 


TELEGRAPH  OFFICE  EQUIPMENT  —  TRAFFIC         l6l 


PROBLEMS 

1.  How  are  the  two  lines  passing  through  a  four-strap  peg  switch 
panel  (see  Fig.  i)  interconnected  at  this  panel  without  introducing 
intermediate  receiving  instruments  into  either  line? 

2.  How  may  a  simplex  line  having  three  loops  at  the  main  switch- 
board give  service  to  three  additional  subscribers  or  brokers'  offices? 

3.  Show  the  connections  at  one  end  of  a  duplex  line  through  the 
main  and  loop  switchboards  and  through  the  distributing  frame, 
when  the  operators  are  stationed  at  an  office  some  distance  away 
from  the  main  telegraph  office.     (Refer  to  circuit  I  of  Fig.  4,  circuit  G 
of  Fig.  6  and  Fig.  16  of  Chap.  II.) 

4.  How  may  the  duplex  line  of  the  preceding  problem  be  tempor- 
arily assigned  to  some' other  branch  telegraph  office? 

5.  Using  the   Confederate  cipher,   the  key  word   "Manchester 
Bluff,"  and  the  index  number  i,  decipher:  YCPNLPDTRTPXCSL. 


CHAPTER  VI 

MISCELLANEOUS  TELEGRAPHS 

i.  Multiplex  Telegraph  Systems.  —  Multiplex  teleg- 
raphy means  the  simultaneous  transmission,  without 
interference,  of  a  plurality  of  messages  in  either  or  both 
directions,  over  a  single  line.  The  duplex,  quadruplex, 
duplex-diplex  and  phantoplex  systems  already  described 
and  also  the  alternating-current  systems  of  Picard  and 
Mercadier  may  be  considered  multiplex  systems,  but  in 
practice  this  name  is  applied  to  those  systems  utilizing 
synchronous  rotation  of  contact  distributors  located  at  the 
two  terminal  stations.  Inasmuch  as  the  maximum  speed 
of  hand  transmission  is  only  about  40  words  per  minute, 
it  is  evident  that  the  speed  possibilities  of  telegraph  lines 
even  with  short  cable  sections  are  not  being  utilized.  With 
the  automatic  telegraph  the  lines  are  more  effectively 
used,  for  speeds  of  250  to  400  words  per  minute  in  each 
direction  are  maintained.  Multiplex  telegraphs  also  con- 
duce to  better  utilization  of  the  lines  and  permit  of  signalling 
at  rates  up  to  about  200  words  per  minute  in  each  direction. 

In  the  Delany  multiplex  system  the  line  is  successively 
assigned  for  short  intervals  to  several  pairs  of  operators 
by  means  of  synchronously  revolving  distributors,  the 
intervals  being  so  short  that  during  the  hand  transmission 
of  a  dot  signal  by  one  operator,  he  has  exclusive  momen- 
tary use  of  the  line  several  times.  Thus,  if  one  pair  of 
operators  receive  the  line  36  times  per  second  and  assum- 

162 


MISCELLANEOUS  TELEGRAPHS  163 

ing  the  average  word  to  have  the  equivalent  of  18  dots, 
signalling  at  the  rate  of  40  words  per  minute  indicates 
3  contacts  per  dot.  Between  these  contacts  the  line  is 
periodically  assigned  to  about  five  other  pairs  of  operators. 
Thus,  each  telegraphic  character  is  made  up  of  short  im- 
pulses rather  widely  separated  as  compared  with  their 
duration.  Such  signals  are  rendered  intelligible  when 
transmitted  by  pole-changing  keys  and  received  by  polar- 
ized relays,  as  in  the  polar  or  bridge-duplex  systems. 

The  Delany  system,  adapted  for  hand  signalling,  was 
used  for  a  number  of  years  but  has  gradually  given  way 
to  the  more  accurate  printing  multiplex  systems.  The 
Rowland  multiplex  page-printing  telegraph,  which  affords 
octuplex  signalling  as  a  quadruple  duplex,  was  for  a  time 
used  on  some  circuits  of  the  Postal  Telegraph-Cable  Com- 
pany and  is  now  being  further  improved.  The  Baudot 
tape-printing  and  the  Murray  page-printing  multiplex 
systems  are  at  present  considerably  used  abroad,  being 
operated  as  double  or  quadruple  duplex  systems.  The 
Murray  multiplex  (§  2)  has  also  begun  its  operation  in  this 
country,  affording  a  speed  of  40  words  per  minute  in  each 
of  eight  channels  over  a  single  wire  between  two  cities 
250  miles  apart.  A  quicker  telegraph  service  is  possible 
with  multiplex  printing  telegraphs  than  with  ordinary 
automatic  transmission  because  of  the  direct  printing  of 
the  received  messages. 

2.   The  Murray  Multiplex  Page-printing  Telegraph.  - 

The  principal  instruments  used  in  the  Murray  multiplex 
telegraph  are  keyboard  tape  perforators,  automatic  trans- 
mitters, distributors  and  electromagnetically-operated 
printers. 


164  TELEGRAPH   ENGINEERING 

The  tapes  are  perforated  according  to  a  special  5-unit 
code,  the  units  for  each  letter,  figure  or  other  character 
being  arranged  transversely  to  the  tape.  The  alphabet 
perforations  are  shown  in  Fig.  i  to  correct  size,  the  letters 
being  separated  by  the  space  character  which  consists 
of  one  perforation  immediately  below  the  guide  hole.  The 
tape  passes  directly  through  a  constant-speed  automatic 
transmitter,  patterned  after  the  Wheatstone  transmitter, 
and  is  then  wound  in  rolls  by  an  automatic  tape-winder. 
The  transmitter  is  provided  with  a  starting  and  stopping 

abcdefahi'jklm 


o  o    o  o  o       o  o 
o    o       o    o  o  o  o 

ooooooooooooooo  oooooooooooooooo 
O  OOO  O  OOO  OOOOO  000  OO 
OOO     OO        OO     O 
O  O  O  O  O 


O     O     O     0000 
OOO        OOO 
ooo  oooooooooooooooooooooooooooo 
OO  OOOOO  OOO  OOOOO  OOOOO 

o  o      o        oo 

OOO        O     OOOOO 


n   o   p   q   r   s   t   u   v   w  x   y   z 
Fig.  i. 

lever  for  use  in  case  the  transmitter  overtakes  the  perfor- 
ating operator. 

The  function  of  the  distributors  is  evident  from  Fig.  2, 
wherein  a  single  line  provides  four  channels  of  communi- 
cation in  either  direction  by  means  of  the  distributor  arms 
D  and  D',  sweeping  over  the  contacts  a,  b,  c  and  d  at 
stations  A  and  B  respectively.  By  joining  duplex  term- 
inal apparatus  to  the  contact  points  at  both  ends  of  the  line 
quadruple  duplex  or  octuplex  signalling  is  rendered  possible. 
Only  one  artificial  line  is  used  at  each  station.  The  con- 
tacts are  preferably  multipled  so  that  a  distributor  arm  con- 


MISCELLANEOUS  TELEGRAPHS 


nects  with  one  duplex  set  several  times  in  one  revolution, 
thereby  reducing  the  rotational  speed  of  these  arms. 

It  is  absolutely  essential  that  both  contact  arms  occupy 
the  same  relative  positions  at  all  times,  that  is,  they  must 
rotate  synchronously.  Such  rotation  is  secured  by  the 


a 
b 

c—0 
•  i   •$ 


D' 


Fig.   2. 


use  of  manually-started  motors  having  tooth-wheel  iron 
armatures  and  periodically  excited  field  magnets,  the  con- 
tact arms  being  mounted  directly  on  the  motor  shaft. 
Periodic  field  excitation  is  obtained  by  the  use  of  reeds 
which  are  kept  vibrating  at  their  natural  frequency.  To 
maintain  synchronism  the  distributor  at  one  station  sends 


DISTRIBUTING 


Fig.  3- 


to  that  at  the  other  station  one  or  more  governing  impulses 
during  each  revolution  of  the  arm,  which  impulses  control 
the  speed  of  the  distant  motor. 

The  circuit  arrangements  for  securing  synchronous  rota- 
tion of  the  distributors  and  for  signalling  over  one  of  the 
communicating  channels  are  schematically  shown  in  Fig.  3, 


l66  TELEGRAPH   ENGINEERING 

the  groups  of  contacts  for  the  other  channels  (that  is,  the 
return  over  a  and  duplex  over  b,  c  and  d  of  Fig.  2),  as 
well  as  the  vibrating  reed  and  distributor  motor  at  station 
A,  being  omitted  for  the  sake  of  clearness.  The  toothed 
wheel  w  of  the  distributor  motor,  when  once  set  in  rotation, 
will  advance  one  tooth  every  time  the  vibrating  reed  r 
makes  one  complete  vibration  due  to  the  impulsive  currents 
reaching  the  magnet  M  every  time  the  reed  touches  its 
front  contact.  The  reed  is  kept  in  vibration  electromag- 
netically  in  the  usual  manner,  that  at  station  B  being 
adjusted  to  operate  one  or  two  per  cent  faster  than  that 
at  A.  Thus  if  distributor  arm  D'  reaches  the  contact 
marked  —  while  the  other  arm  D  is  still  on  the  contact 
marked  +,  a  current  pulse  from  battery  B  will  flow  over 
the  line  and  through  the  polarized  relay  P  in  such  direc- 
tion as  to  close  the  contact  of  this  relay.  This  momentary 
contact  enables  battery  Bf  to  actuate  the  governing  relay 
R  and  open  the  vibrator  circuit  for  an  instant,  thereby 
retarding  slightly  the  vibration  of  the  reed  and  the  rota- 
tion of  the  distributor  arm  D'.  If  both  arms  were  to  pass 
over  the  —  contacts  simultaneously,  the  contact  of  the 
polarized  relay  would  be  open  and  no  governing  impulse 
would  reach  relay  R. 

Thereafter,  the  two  distributor  arms  pass  together  succes- 
sively over  the  main  contacts  i,  2,  3,  4  and  5,  and  then  over 
similar  sets  of  contacts  for  the  other  transmitting  chan- 
nels (not  shown).  The  polarity  of  the  five  current  pulses 
sent  out  jipon  the  line  at  station  A  depends  upon  the 
positions 'of  the  rocking  pins  which,  in  turn,  depend  upon 
the  tape  perforations,  as  in  the  Wheatstone  transmitter, 
the  various  permutations  of  positive  and  negative  pulses 
corresponding  to  the  various  letters  and  other  characters  to 


MISCELLANEOUS  TELEGRAPHS  167 

be  transmitted.  At  station  B  the  five  main  contacts  are 
connected  to  an  equal  number  of  distributing  relays  which 
select  the  particular  printer  magnets  in  a  manner  very 
similar  to  that  explained  with  the  aid  of  Fig.  16  of  Chap.  IV. 
As  the  contact  arm  passes  over  the  contact  x,  the  print- 
ing magnet  is  energized,  causing  the  printing  on  the  receiver 
message  blank  of  that  letter  whose  printer  magnet  was  se- 
lected by  the  distributing  relays. 

From  the  foregoing  it  will  be  understood  how  this  method 
of  signalling  can  be  extended  to  give  quadruple-duplex  or 
possibly  even  sextuple-duplex  transmission  over  a  single- 
line  wire,  the  received  characters  over  each  communicating 
channel  being  directly  printed.  Messages  requiring  retrans- 
mission to  remote  places  may  be  directly  perforated  in 
tapes  at  the  intermediate  station,  the  five  magnets  that 
set  the  punches  of  the  receiving  perforator  being  connected 
in  series  with  the  corresponding  distributing  relays  of  the 
printer. 

3.  The  Pollak-Virag  Writing  Telegraph.  —  The  Pollak- 
Virag  rapid  telegraph  system  has  been  installed  on  a  num- 
ber of  European  telegraph  lines  and  affords  signalling  at 
rates  up  to  700  words  per  minute  over  two-wire  lines. 

Tape  transmission  is  utilized  in  the  Pollak-Virag  writing 
telegraph,  the  perforations  for  the  various  characters  being 
of  various  sizes  and  located  in  one  or  more  of  six  rows. 
The  paper  tape  is  prepared  on  a  keyboard  perforator,  all 
the  perforations  for  a  letter  or  other  character  being  made 
by  a  single  depression  of  a  key.  The  tape  is  passed  over 
a  motor-driven  drum  D,  Fig.  4,  which  is  formed  of  six 
electrically-distinct  rings.  Two  brushes,  b  and  &',  each 
spanning  three  rings,  press  the  tape  against  the  drum  and 


i68 


TELEGRAPH   ENGINEERING 


make  contact  with  its  rings  through  the  perforations, 
the  duration  of  contact  depending  upon  the  size  of  the 
perforation.  Rings  i,  2  and  3  connect  to  battery  B  so 
that  brush  b  and  the  upper  line  wire  may  have  a  potential 
with  respect  to  the  other  line  wire  of  say  +  50,  +  30  or 

—  30  volts  respectively.     Similarly,  rings  4,  5  and  6  con- 
nect to  battery  Bf  so  that  brush  bf  and  junction  x  may  have 
a  potential  with  respect  to  ground  of  say  -f  30,  —  30  and 

—  50   volts   respectively.     Combinations    of    contacts    of 
different  durations  and  in  correct  sequence  with  these  six 
rings  occasion  current  pulses  in  the  line  which  actuate  a 


RECEIVER 


Fig.  4. 

specially-designed  receiver  to  produce  in  script  the  various 
letters  and  figures. 

The  receiving  instrument  resembles  two  telephone  re- 
ceivers (R  and  Rf,  Fig.  4)  whose  diaphragms  are  placed 
in  one  plane.  In  front  of  the  diaphragms  is  mounted  a 
permanent  magnet,  from  the  center  and  ends  of  which 
project  soft  iron  strips  with  forwardly-extending  pointed 
tips.  A  small  soft  iron  sheet  carrying  the  mirror  m  (shown 
in  the  lower  right  corner)  is  magnetically  held  against  the 
three  tips.  The  motions  of  the  two  diaphragms  of  re- 


MISCELLANEOUS  TELEGRAPHS  169 

ceivers  R  and  Rf  are  transmitted  by  means  of  links  to  the 
tips  t  and  /'  respectively,  which  are  located  i  mm.  above 
and  to  the  left  of  the  center  tip  c  respectively.  Therefore, 
if  the  diaphragm  of  receiver  R  vibrates  the  mirror  will 
rotate  about  a  horizontal  axis,  and  if  the  other  diaphragm 
vibrates  the  mirror  will  rotate  about  a  vertical  axis.  If 
both  vibrate,  the  mirror  will  describe  the  motion  of  the 
resultant  vibration. 

A  small  pencil  of  light  issuing  fr6m  an  electric  light  / 
impinges  upon  the  mirror  and  is  reflected  as  a  spot  of  light 
upon  a  band  of  photographic  paper  p.  A  revolving 
opaque  hood  H  having  a  helical  slit  encloses  the  lamp  so 
that  the  spot  of  light  will  advance  from  one  side  of  the 
paper  to  the  other,  and  then  jump  to  the  next  line,  and  so 
on.  If  the  mirror  vibrates  in  accordance  with  transmitted 
impulses,  its  motions  will  be  properly  recorded.  After 
exposure,  the  sensitive  paper  travels  down  through  solu- 
tions which  develop  and  fix  the  paper  in  about  15  seconds, 
revealing  legible  script. 

The  two-line  wires  join  with  the  terminals  of  the  winding 
of  receiver  R,  which  is  actuated  by  portions  of  the  battery 
B,  this  receiver  forming  all  vertical  components  of  the 
transmitted  characters.  Both  line  wires  are  used  as  a 
single  conductor  for  the  other  receiver  circuit  by  means 
of  the  neutral  points  xt  formed  by  a  high-resistance  shunt 
at  the  transmitter,  and  y,  the  mid-point  of  the  winding  of 
receiver  R.  In  this  way  battery  B'  actuates  receiver  R' 
(ground  being  the  return  path),  this  receiver  forming  all 
horizontal  components  of  the  characters.  In  order  to 
abolish  the  disturbing  influences  of.  resistance,  inductance 
and  capacity  when  signalling  over  long  lines,  various  con- 
densers and  reactors  may  be  introduced  at  particular  places 


iyo 


TELEGRAPH   ENGINEERING 


in  the  circuit.  Condensers  connected  in  parallel  with 
the  receivers  R  and  Rf  are  introduced  to  soften  the  action 
of  the  currents.  Synchronous  rotation  of  the  hood  at 
the  receiver  and  the  drum  at  the  transmitter  is  not  neces- 
sary in  this  system. 

The  nature  of  the  perforations  and  the  corresponding 
received  script  is  indicated  in  Fig.  5  for  the  word  "  message. " 
The  direction  and  relative  magnitudes  of  the  impressed 
voltages  are  indicated  at  the  left,  and  the  received  graph 
for  only  the  vertical  components  is  shown  immediately 


o  o       0 

—         1"    -" -t  "-      ~     ~          •       "      ™ 


__/lA/l/^j/l^^ 


i    i     i 

Fig.  5. 

below  the  tape.  The  actual  received  trace,  which  corre- 
sponds to  both  vertical  and  horizontal  movements,  is 
shown  at  the  bottom. 

4.  The  Telautograph.  —  The  telautograph  is  an  instru- 
ment for  the  electrical  reproduction  of  handwriting  at  a 
distance,  invented  by  Prof.  Elisha  Gray  and  perfected  by 
Geo.  S.  Tiffany,  and  consists  of  a  transmitter  and  a  receiver. 
The  appearance  of  the  instrument  made  by  the  Gray 
National  Telautograph  Company  is  shown  in  Fig.  6.  These 


MISCELLANEOUS  TELEGRAPHS 


171 


devices  may  be  operated  singly  over  a  private  line  or  con- 
nected through  a  switchboard  so  as  to  enable  any  two 
instruments  to  be  used  together.  Also,  a  single  transmitter 
may  be  arranged  to  operate  a  number  of  receivers  simul- 
taneously. 

At  the  transmitter  the  pencil  is  attached  by  a  system 
of  levers  to  two  contact  rollers  which  bear  against  the  inner 


Fig.  6. 

surfaces  of  two  curved  rheostats,  which  are  connected  across 
direct-current  supply  mains,  usually  of  115  volts.  The 
potential  difference  between  either  end  of  each  rheostat 
and  the  accompanying  roller  varies  with  the  position  of 
this  roller,  which  position  changes  in  writing.  These  vary- 
ing voltages  are  impressed  on  circuits  which  extend  to  the 


172 


TELEGRAPH   ENGINEERING 


receiver,  where  they  terminate  in  coils  wound  on  copper 
bobbins  and  arranged  to  move  horizontally  within  intense 
magnetic  fields  against  the  action  of  springs.  In  operation 
the  two  coils  are  displaced  in  proportion  to  the  forces  acting 
on  them,  which  forces  are  proportional  to  the  currents 
traversing  the  coils,  which  currents  vary  with  the  im- 
pressed voltages,  and  which,  in  turn,  depend  upon  the  dis- 
placements of  the  transmitting  rollers  from  their  zero 
positions,  thereby  rendering  the  displacement  of  each  coil 
proportional  to  that  of  the  corresponding  roller.  The  coils 
at  the  receiver  are  connected  by  a  system  of  levers  which 
actuates  the  recording  pen,  the  lever  system  being  similar 
to  that  at  the  transmitter.  Thus,  the  motion  of  the  pen 
is  the  resultant  of  the  motions  of  the  two  coils,  which  mo- 
tions are  proportional  to  those  of  the  transmitting  contact 
rollers,  and  they  are  the  component  motions  of  the  trans- 
mitting pencil;  therefore,  the  receiving  pen  duplicates 
the  motions  of  the  transmitting  pencil. 

The  simplified  scheme  of  connections  of  the  improved 
transmitter  and  receiver  is  shown  in  Fig.  7,  which  also 


PAPER  SHIFTER 

So 


PAPERM8rdFNTETR   RECEIVER 


TRANSMITTER 


Fig.  7. 


indicates  the  various  auxiliary  devices  utilized  in  realizing 
commercial  practicability.  The  apparatus  used  for  the 
transmission  of  the  writing  motions  is  apparent,  the  left 


MISCELLANEOUS  TELEGRAPHS  173 

and  right  rollers  on  the  transmitter  rheostats  connecting 
directly  with  the  two  corresponding  receiver  coils  that  are 
located  in  separate  annular  air  gaps  of  one  magnetic  cir- 
cuit. The  two  pairs  of  power  terminals  connect  to  com- 
mercial electrical  supply  mains. 

The  functions  of  the  auxiliary  devices  are  as  follows:  - 
The  master  switch  controls  the  paper  shifter  magnet  which 
operates  a  clamp  that  pulls  the  paper  through  one  line 
space  over  the  transmitter  platen.  Shifting  of  the  receiver 
paper  is  similarly  accomplished,  the  shifting  magnet  being 
locally  energized  through  the  contacts  of  the  relay  which 
is  included  in  one  of  the  two  line  wires  and  which  is  like- 
wise under  the  control  of  the  master  switch. 

This  relay  also  serves  to  complete  the  circuit  of  the  elec- 
tromagnet which  develops  the  magnetic  field  for  the 
receiver  coils.  It  will  be  observed  that  the  winding  on 
the  lower  bobbin  may  be  periodically  short-circuited  by  the 
spring  armature  of  a  vibrator.  This  action  causes  the 
intensity  of  the  magnetic  field  to  flicker  rapidly  and  pro- 
duces a  minute  vibration  in  the  receiver  coils.  Friction  of 
the  pen  on  the  paper  and  in  the  moving  parts  of  the  re- 
ceiver is  greatly  reduced  by  this  vibration,  and  conse- 
quently the  pen  is  very  sensitive  to  small  changes  in  the 
line  currents.  Although  small  alternating  currents  are  in- 
duced in  the  coils  by  this  vibratory  motion,  the  pen-lifting 
relay  bridged  across  the  line  wires  will  not  operate,  because 
of  the  equality  of  these  opposing  currents. 

Pen  lifting  is  accomplished  at  the  receiver  by  means  of 
a  locally-operated  magnet-  placed  back  of  the  receiver 
writing  platen,  the  armature  carrying  a  rod  adapted  to 
move  the  pen  arms  and  lift  the  pen  away  from  the  paper 
when  the  magnet  is  energized.  This  pen-lifter  magnet  is 


174  TELEGRAPH   ENGINEERING 

controlled  by  a  pen-lifting  relay  that  has  a  peculiarly 
constructed  armature  which  is  set  into  violent  vibration 
and  makes  imperfect  contact  with  its  contacts  points 
when  alternating  current  passes  through  the  relay  winding, 
but  which  armature  is  quiescent  and  makes  good  contact 
with  its  contact  points  when  no  current  traverses  the 
winding.  At  the  transmitter  the  secondary  winding  of 
a  small  induction  coil  is  bridged  across  the  line  wires  through 
two  condensers,  and  the  primary  winding  derives  its 
energy  from  the  power  mains  through  a  vibrating  armature. 
A  contact  beneath  the  writing  platen  is  arranged  to  short- 
circuit  the  vibrator  when  the  platen  is  not  depressed. 
Thus,  during  intervals  when  no  characters  are  written 
no  electromotive  force  is  induced  in  the  secondary  winding 
of  the  coil,  no  current  traverses  the  pen-lifting  relay  and 
consequently  the  circuit  of  the  pen-lifter  magnet  is  closed, 
thereby  lifting  the  pen  away  from  the  paper.  Depression 
of  the  platen  by  the  transmitter  pencil  in  writing,  per- 
mits operation  of  the  vibrator  and  occasions  an  alternating 
electromotive  force  in  the  secondary  winding  of  the  coil. 
This  induced  voltage  develops  a  current  that  traverses  the 
two-line  wires  simultaneously  with  the  "writing"  currents 
and  also  traverses  the  pen-lifting  relay.  The  armature  of 
this  relay  is  thereby  agitated  so  that  the  pen-lifter  magnet 
is  effectively  open-circuited,  and  the  release  of  its  armature 
permits  the  receiving  pen  to  touch  the  paper. 

Ink  for  the  receiving  pen  is  contained  in  a  small  stoppered 
bottle  with  an  orifice  near  the  bottom,  the  ink  being  re- 
tained by  atmospheric  pressure.  When  the  telautograph 
is  idle,  retractile  springs  hold  the  pen  in  the  ink  at  this 
orifice.  In  order  to  close  the  master  switch  it  is  necessary 
to  bring  the  transmitting  pencil  to  a  position  corresponding 


MISCELLANEOUS  TELEGRAPHS 


175 


to  that  of  the  pen  and  to  press  the  pencil  on  a  button  there 
located,  thereby  releasing  a  catch  that  holds  the  master 
switch.  This  process  is  repeated  for  each  paper-shifting 
operation  so  that  sudden  large  movements  of  the  receiving 
pen  are  avoided. 

5.  Telephotography.  —  The  electrical  transmission  of 
photographs  from  one  place  to  another,  called  telephotog- 
raphy, may  be  accomplished 
by  utilizing  the  property  of 
the  element  selenium  by  vir- 
tue of  which  it  varies  its 
electrical  resistance  under 
the  influence  of  light.  The 
lowering  of  selenium  resist- 
ance with  increasing  inten- 
sity of  white  light  is  shown 
in  Fig.  8  for  three  different 


160 


120 


80 


40 


80 


160 


240 


320 


Fig.  8. 


"cells,"  which  are  metallic 
grids  properly  coated  with  selenium.  Intensity  of  illumi- 
nation is  expressed  in  luces  (sing,  lux),  the  lux  being  the 
intensity  of  light  at  one  meter's  distance  from  a  standard 
candle.  The  resistance  R  of  a  cell  under  illumination  / 
can  be  conveniently  expressed  as 


where  c  is  a  constant  depending  upon  the  selenium  cell, 
and  n  is  an  exponent  whose  value  depends  upon  the  dura- 
tion of  exposure  and  wave-length  of  light,  and  lies  between 
0.25  and  i.o.  The  resistance  change  in  selenium  with  light 
variation  is  not  instantaneous,  but  most  of  this  change 


i76 


TELEGRAPH   ENGINEERING 


occurs  during  the  first  few  instants,  as  indicated  in  Fig.  9, 
which  represents  a  three  minutes  exposure  of  cell  B  to 
light  of  ico  luces  intensity,  with  subsequent  recovery. 

Dr.  Korn  has  perfected  telephotographic  apparatus 
which  is  in  successful  practical  operation  over  several  long 
distance  lines. 

The  complete  apparatus  for  a  station  consists  of  a  trans- 
mitter and  a  receiver  mounted  together,  each  having  a 
long  tube  through  which  light  from  the  lamps  at  one  end, 
passes  to  the  rotating  cylinders  at  the  other.  The  princi- 


pal details  of  the  improved  Korn  transmitter  and  receiver 
are  shown  in  Figs.  10  and  1 1  respectively. 

In  the  transmitter  the  Nernst  lamp  L  sends  out,  through 
lens  A,  a  beam  of  light  which  is  received  upon  the  dia- 
phragm g,  after  passing  through  lens  G.  The  diaphragm 
serves  to  concentrate  the  light  to  a  point  upon  the  glass 
cylinder,  around  which  is  placed  the  photograph  in  the 
shape  of  a  positive  film,  the  cylinder  being  mounted  upon 
the  rotating  shaft  V.  The  beam  of  light  passes  through 
the  photographic  film  and  is  reflected  upward  within  the 


MISCELLANEOUS  TELEGRAPHS 


177 


cylinder  by  the  prism  P  and  impinges  upon  the  selenium 
cell  Si.  The  cylinder  T,  in  addition  to  its  rotary  motion, 
has  an  axial  movement,  so  that  all  parts  of  the  photo- 


TRAN8MITTER 


Fig.  10. 


graph  successively  pass  the  point  of  light.  As  the  cylinder 
revolves,  the  illumination  on  the  selenium  cell  will  change, 
thus  sending  a  current  of  variable  intensity  to  the  receiver. 


Fig.  xz. 

The  receiver,  Fig.  n,  is  provided  with  a  Nernst  lamp  Lf 
which  sends  out  a  beam  of  light  through  the  galvanometer 
shutter  b.  This  galvanometer,  called  a  light-relay,  con- 
sists of  an  electromagnet  d,  provided  with  long  perforated 


178  TELEGRAPH  ENGINEERING 

pole-pieces  pp,  between  which  is  placed  the  moving  ele- 
ment M.  This  consists  of  a  double  fine  platinum  wire 
under  tension,  carrying  a  small  sheet  of  aluminium  foil  b. 
When  a  current  flows  through  the  wire,  the  electromagnet 
being  separately  excited,  the  aluminium  sheet  is  deflected 
to  one  side  and  the  amount  of  the  deflection  is  propor- 
tional to  the  current  flowing.  Thus,  the  intensity  of  the 
beam  of  light  which  passes  through  the  light-relay  to  the 
cylinder  R  depends  upon  the  current  in  the  line.  The 
cylinder  is  mounted  on  a  revolving  shaft  W,  which  has 
also  an  axial  movement,  so  that  all  parts  of  the  cylinder 
surface  are  brought  successively  under  the  point  of  light 
emerging  from  the  diaphragm.  Thus,  the  variable  current 
coming  from  the  transmitter  causes  a  corresponding  varia- 
tion in  the  amount  of  light  incident  upon  the  receiving 
cylinder,  and  an  exact  reproduction  of  the  original  photo- 
graph may  be  obtained  upon  developing  the  received 
image. 

It  is  necessary  for  the  proper  operation  of  this  apparatus 
that  the  resistance  change  of  the  selenium  cell  be  rapid 
so  that  it  will  respond  almost  immediately  to  the  variations 
of  light  incident  upon  it.  Such  quick  action  is  secured  by 
the  use  of  a  second  selenium  cell  connected  with  the  cell  of 
the  transmitter,  so  that  the  resultant  conductivity-time 
curve  of  both  rises  quickly  at  the  start  and  falls  quickly 
upon  darkening  the  cell.  As  the  receiver  of  a  station  is 
not  in  use  when  sending,  the  light-relay  of  the  receiver  can 
be  employed  in  this  connection,  as  shown  in  Fig.  n.  In 
the  bottom  of  the  vertical  mirror-lined  chamber  is  the  cell 
Sz,  which  receives  illumination  from  the  lamp  L'  by  means 
of  the  reflecting  prism  P' .  To  secure  a  diffused  light  upon 
this  selenium  cell,  a  series  of  glass  cylindrical  rods  is  inter- 


MISCELLANEOUS  TELEGRAPHS 


179 


posed  at  r.  When  the  transmitter  cell  6*1,  Fig.  10,  is  illu- 
minated, a  current  flows  through  the  home  light-relay 
deflecting  its  shield,  and  thus  gives  the  compensating  cell 
62  a  corresponding  illumination.  The  two  cells  are  con- 
nected in  opposition,  and  the  resulting  current  variation 


s, 


s, 


LINE  TO 

LIGHT  RELAY 

OF  DISTANT 

RECEIVER 


Fig.  12. 

corresponds   very   closely   with    the   variations   of   light, 
owing  to  the  fact  that  the  two  cells  are  selected  to  give  dif- 
ferent resistance  changes  under  the  same  illumination. 
The  method  of  connecting  the  selenium  cells  is  shown  in 


Fig.  12.  The  shape  of  the  differential  current  which  flows 
between  x  and  y  is  shown  in  Fig.  13,  in  which  the  con- 
ductivity-time curve  of  each  cell  is  indicated,  one  above 
and  the  other  below  the  datum  line.  As  cell  52  is  not 
illuminated  as  soon  as  cell  Si,  its  curve  will  begin  shortly 


l8o  TELEGRAPH  ENGINEERING 

after  that  of  the  latter.  As  will  be  observed,  the  time  of  rise 
and  decay  of  current  are  practically  identical,  and  the  rate 
of  change  is  exceedingly  rapid.  The  use  of  the  compensat- 
ing cell  results  in  a  considerable  gain  in  photographic  detail. 

As  the  normal  swing  of  the  light-relay  is  from  o.oi  to 
0.02  second,  a  rapid  variation  of  current  is  permissible, 
and  the  cylinder  at  the  transmitting  end  can,  therefore, 
be  rotated  very  rapidly.  At  present  a  photograph  9  inches 
by  6  inches  can  be  reproduced  in  less  than  12  minutes,  the 
size  of  the  received  image  being  4  inches  by  2^  inches. 

It  is  obvious  that  the  cylinder  at  the  transmitting  station 
and  that  at  the  receiving  station  must  revolve  at  the  same 
speed,  otherwise,  no  image  reproduction  could  be  obtained. 
The  speed  of  the  receiving  cylinder  is  adjusted  to  be 
about  one  per  cent  faster  than  that  of  the  transmitter. 
The  former  is  brought  to  a  stop  at  the  end  of  each  revolu- 
tion, and  when  the  transmitter  cylinder  has  finished  its 
revolution,  a  current  impulse  of  the  reverse  direction  is 
sent  to  the  receiving  station  actuating  a  relay  there  and 
releasing  the  cylinder.  Both  cylinders  then  start  up 
together  upon  the  next  revolution. 

A  modification  of  the  light-relay  has  lately  been  intro- 
duced by  Korn,  called  a  step-relay,  for  controlling  weak 
high-frequency  currents  which  serve  to  initiate  high-tension 
arcs.  The  currents  so  started  are  either  sent  directly  over 
the  line  to  affect  the  receiver,  or  are  used  to  furnish  a  per- 
forated tape  corresponding  to  the  picture  for  affecting  its 
transmission  at  suitable  speed.  He  has  also  devised  an- 
other transmitting  method  which  dispenses  with  selenium 
cells  and  thereby  permits  of  larger  line  currents.  This 
method  employs  a  photographically-prepared  copper  sheet 
upon  which  are  formed  parallel  striations  of  gelatin  in 


MISCELLANEOUS  TELEGRAPHS 


181 


greater  or  less  widths  depending  upon  the  darkness  or 
brightness  of  the  various  parts  of  the  image  to  be  trans- 
mitted. This  sheet  is  placed  around  a  metal  cylinder,  and 
as  it  revolves  and  also  advances  axially,  a  metal  stylus  trav- 
erses the  striations  and  causes  contact  to  be  broken  for  long 
or  short  intervals  in  accordance  with  the  width  of  the  stria- 
tions. The  resulting  intermittent  currents  pass  through  the 
light-relay  at  the  receiver  and  reproduce  the  image  as  before. 
Marino  has  developed  a  system  of  color  telephotography 
which  utilizes  the  sustained  high-frequency  electrical 
oscillations  derived  from  three  direct-current  arcs  that  are 
shunted  by  condensers  and  inductances.  These  Thomson 


arcs  are  arranged  to  produce  oscillations  of  different  fre- 
quencies whose  amplitudes  are  controlled  by  seven  sele- 
nium cells,  every  cell  being  most  sensitive  to  one  of  the 
seven  primary  colors.  At  the  receiver  these  oscillations 
control  other  arcs  connected  in  circuits  that  are  tuned  to 
the  respective  frequencies.  The  manner  in  which  color 
variations  are  transmitted  in  this  system  is  indicated  in 
Fig.  14. 

A  long  opaque  diaphragm  d,  with  properly  placed  aper- 
tures of  about  i  mm.  diameter,  passes  uniformly  in  front 
of  an  illuminated  plate  P  bearing  the  picture  to  be  trans- 
mitted. These  apertures  are  spaced  transversely  about 


182  TELEGRAPH   ENGINEERING 

i  mm.  apart  and  longitudinally  a  distance  equal  to  the 
width  of  the  plate,  therefore  light  from  every  point  of  the 
picture,  after  passing  through  a  lens,  falls  successively 
on  the  prism  p.  Each  ray  is  dispersed  by  the  prism,  and 
impinges  upon  the  set  of  selenium  cells  S  located  so  that 
each  cell  receives  light  of  one  color,  thereby  actuating  one 
or  more  of  the  cells  according  to  its  constituent  colors. 
These  cells  are  in  three  groups,  each  group  with  a  battery 
being  bridged  across  the  inductance  (L,  U  or  Z/')  connected 
in  the  supply  circuit  of  the  arc  (a,  a'  or  a"\  Variations 
in  the  resistances  of  the  selenium  cells  modulate  the  voltages 
across  the  arcs  and  consequently  affect  the  amplitudes  of 
the  oscillations  that  are  developed  in  the  three  condensive 
circuits.  These  oscillations  induce  corresponding  currents 
in  the  line  coils  /,  and  are  superimposed  upon  each  other 
to  form  the  line  current. 

At  the  receiver  the  three  component  oscillations  of  the 
line  current  are  sorted  out  by  means  of  the  tuned  oscillatory 
circuits  c,  c'  and  c",  and  are  rectified  by  audion  or  crystal 
detectors  D,  D'  and  D" .  The  detectors  vary  the  potential 
difference  of  the  three  receiving  arcs  A,  A'  and  A",  and 
consequently  vary  their  brilliancy.  In  front  of  the  arcs 
are  colored  screens  —  s,  a  mixture  of  red  and  orange;  s',  a 
mixture  of  yellow,  green  and  blue;  and  s",  a  mixture  of 
indigo  and  violet  —  the  emitted  rays  from  all  three  arcs 
being  recombined  and  focussed  upon  a  particular  point  of 
the  receiving  plate  R.  Each  resulting  beam  is  therefore 
rendered  identical  in  color  variations  and  intensity  with 
the  original. 

6.  Television.  —  The  property  of  selenium  of  varying 
its  resistance  under  the  influence  of  light  is  also  utilized 


MISCELLANEOUS  TELEGRAPHS  183 

in  experiments  to  attain  a  practical  method  of  seeing  at 
a  great  distance  by  means  of  a  connecting  wire  or  wires. 
Numerous  such  systems  of  television  have  been  patented; 
indeed  elementary  geometrical  patterns  have  been  success- 
fully transmitted  by  Ruhmer  between  Brussels  and  Liege, 
a  distance  of  72  miles,  his  transmitter  consisting  of  25  sele- 
nium cells,  each  about  5  centimeters  square. 

Rignoux  and  Fournier  have  developed  a  system  of 
television,  involving  the  employment  of  a  multitude  of 
cells  but  employing  only  two  connecting  wires  between 
the  stations.  The  currents  from  the  various  circuits  are 
taken  successively  by  a  rapidly  rotating  collector  arm  at 


<k 


^—^ — •*-£&- -> 


LINE 
WIRES 


© 


Fig.  15. 


the  transmitting  station  and  supplied  to  the  two-line  wires. 
The  principle  of  the  receiving  device  is  based  upon  the 
Faraday  effect.  The  arrangement  of  the  apparatus  at 
this  station  is  shown  in  Fig.  15,  in  which  L  is  a  source  of 
light  whose  rays  are  polarized  by  the  prism  P  and  then 
traverse .  a  tube  T  containing  water,  or  better,  carbon 
bisulphide.  A  second  Nicol  prism  P'  is  so  rotated  about 
the  direction  of  the  light  ray  as  an  axis  that  the  polarized 
light  cannot  pass  through  it,  and  is  then  fixed  in  this 
position.  If  a  current  flows  through  the  electromagnet  E 
which  surrounds  the  tube  filled  with  liquid,  the  angle  of 
polarization  changes  and  the  prism  P'  no  longer  prevents 


1 84  TELEGRAPH  ENGINEERING 

the  light  from  passing  through  it.  Thus,  a  beam  of  light 
of  varying  intensity,  corresponding  to  the  illumination  of 
the  particular  selenium  cell  connected  at  that  instant 
with  the  line  wires,  falls  upon  the  cylinder  C,  which  rotates 
in  synchronism  with  the  collector  arm  at  the  transmitting 
station.  This  cylinder  carries  a  number  of  small  mirrors 
m,  which  are  so  arranged  that  the  light  reflected  from  each 
falls  on  a  particular  part  of  the  screen  S.  On  this  screen 
is  therefore  formed  a  picture,  consisting  of  patches  of 
various  degrees  of  brightness,  of  the  object  exposed  at  the 
transmitter.  The  different  parts  of  the  picture,  although 
projected  successively,  will  appear  simultaneous,  if  the 
entire  picture  is  produced  within  a  fraction  of  a  second. 
An  indefinite  repetition  of  this  process  yields  a  persistent 
picture. 

In  Low's  system  of  television  the  received  currents  mag- 
netically control  the  positions  of  slots  which  admit  light 
to  squares  on  the  receiving  screen  that  are  located  in  the 
same  positions  as  the  corresponding  selenium  cells  at  the 
transmitter. 

7.  Military  Induction  Telegraphs. —  In  times  of  war 
crudely-constructed  pole  lines  and  often  short  lines  of  bare 
wire  laid  on  the  ground  are  utilized  in  the  telegraphic  trans- 
mission of  military  information.  Because  of  the  low  insu- 
lation resistance  of  such  lines,  and  because  of  the  difficulty 
of  transporting  means  for  the  production  of  electricity,  the 
ordinary  simplex  signalling  methods  are  not  used,  but,  in- 
stead, signalling  by  means  of  induced  currents  at  high 
voltage  is  employed.  Such  induction  telegraphy  permits 
of  signalling  over  distances  of  about  300  miles  with  only 
3  to  6  dry  cells. 


MISCELLANEOUS  TELEGRAPHS  185 

The  circuit  of  an  induction  telegraph  includes  the  sec- 
ondary winding  of  an  induction  coil  at  each  station,  the 
primary  winding  being  joined  to  a  local  circuit  with  a  key 
and  battery.  A  current  pulse  is  induced  in  the  secondary 
coil  whenever  the  primary  circuit  is  made  or  broken,  but 
no  steady  current  is  induced  either  when  the  key  is  kept 
open  or  when  kept  closed.  Since  the  direction  of  the  sec- 
ondary momentary  current  when  the  primary  circuit  is 
broken  is  opposite  to  that  when  the  primary  circuit  is 
closed,  it  will  be  observed  that  a  polarized  receiving  in- 
strument is  essential  for  the  operativeness  of  this  type  of 
telegraph  circuit.  Using  step-up  induction  coils,  high  line 
voltages  may  be  availed  of  with  few  cells,  thereby  render- 
ing induction  telegraphs  admirably  suited  for  military  pur- 
poses even  for  fairly  long  lines. 

The  United  States  army  induction  telegraph  field  kit 
includes  a  polarized  receiving  instrument,  a  key,  several 
dry  cells  and  an  induction  coil,  mounted  in  a  portable 
box.  The  induction  coil  has  100  times  as  many  turns  on 
the  secondary  as  on  the  primary  winding,  and  takes  about 
12  watts  at  4  volts.  The  circuit  of  a  simplex  induction 
telegraph  is  shown  in  Fig.  16,  in  which  P,  Pf  are  polarized 
relays,  5,  Sf  are  sounders,  B,  B'  are  local  batteries,  K,  K' 
are  keys,  and  p  and  s  are  respectively  the  primary  and  sec- 
ondary windings  of  the  induction  coils  /,  /'.  Upon  de- 
pressing the  key  K,  an  induced  current  of  momentary 
duration  will  be  produced  in  the  secondary  winding  of  in- 
duction coil  /,  flowing,  say,  upward,  which  current  in  flow- 
ing through  the  two  polarized  relays  to  ground  G'  at  the 
distant  station  causes  their  armatures  to  touch  the  sounder 
contacts.  Both  sounders  will  operate  as  the  result  of  the 
completion  of  their  local  circuits.  Although  the  current 


i86 


TELEGRAPH  ENGINEERING 


pulse  over  the  line  is  of  very  short  duration,  the  polarized 
relay  armatures  will  remain  against  their  sounder  contacts 
until  the  key  is  released.  The  subsequent  opening  of  key 
K  produces  a  reverse  current  pulse  through  the  line  and 
the  relay  windings,  which  causes  the  relay  armatures  to 
open  their  respective  sounder  circuits.  Signalling  in  the 
opposite  direction  may  be  accomplished  similarly. 

To  reduce  further  the  impedimenta  during  warfare,  the 
polarized  relay  and  local  sounder  are  replaced  by  a  polar- 
ized sounder  in  induction  telegraph  sets  devised  by  G.  R. 


Fig.  16. 


Guild  for  use  by  the  United  States  Signal  Corps.  Such 
sounders  resemble  those  of  the  usual  type  except  in  that 
the  soft-iron  yokes  joining  the  lower  ends  of  the  magnet 
cores  are  replaced  by  permanent  horseshoe  magnets, 
thereby  giving  a  definite  polarity  to  the  poles  of  the  electro- 
magnet cores.  A  current  through  the  coils  will  cause  the 
armature  to  be  more  or  less  strongly  attracted  according 
as  the  electromagnetization  assists  or  opposes  that  of  the 
permanent  magnet.  The  retractile  spring  of  the  polarized 
sounder  is  adjusted  so  that  reversal  of  current  direction 
will  effect  its  proper  operation  with  currents  as  small  as 
10  milliamperes.  Inasmuch  as  these  instruments  may  be  dif- 


MISCELLANEOUS  TELEGRAPHS 


I87 


f erentially  wound  (shown  at  PS  in  Fig.  1 7) ,  they  may  be  used 
advantageously  for  duplex  induction  telegraphic  signalling. 
Induction  telegraph  repeaters  are  used  for  repeating  into 
simplex  closed-  or  open-circuit  lines  or  into  another  induc- 
tion telegraph  circuit.  Fig.  17  shows  the  arrangement  for 
repeating  from  an  induction  telegraph  to  a  closed-circuit 
simplex  line,  and  vice  versa,  using  polarized  and  polarized- 
repeating  sounders.  The  position  of  the  armatures  corre- 
sponds to  the  normal  condition  for  no  transmission  of  mes- 
sages. The  arrows  a  and  a'  indicate  the  direction  of  the 
induced  currents  in  the  line  circuit  on  the  closing  of  the 
local  circuits  including  batteries  B  and  bf  respectively. 
The  armature  of  the  polarized  repeating  sounder  PR2  is 
biased  to  remain  on  its  lower  contact  except  when  a  current 
flows  through  either  of  its  coils.  The  letters  n  and  s  indi- 
cate the  polarity  of  the  polarized  sounders  which  is  occa- 
sioned by  their  permanent  magnets.  The  opening  of  the 


Fig.  17. 

armature  contact  of  the  other  repeating  sounder  PRi  re- 
moves the  short-circuit  from  the  left-hand  coil  of  repeater 
PR2,  thereby  energizing  this  coil,  but  at  the  same  time  the 
introduction  of  its  resistance  reduces  the  current  strength 
in  relay  R  to  a  value  insufficient  to  keep  its  armature  at- 
tracted. The  repeating  of  signals  in  either  direction  may 
readily  be  traced  (see  problem  5). 


l88  TELEGRAPH  ENGINEERING 


PROBLEMS 

1.  Decipher  the  tape  shown  below,  which  represents  part  of  a 
message  transmitted  by  the  Murray  multiplex  telegraph. 

2.  If  operators  can  perforate  transmitting  tapes  at  the  rate  of 
only  4  letters  per  second,  how  many  operators  would  be  required  to 
keep  the  transmitters  at  one  station  of  the  Murray  quadruple-duplex 
and  of  the  Pollak-Virag  writing  telegraphs  supplied  if  their  trans- 
mitters are  operated  at  40  and  700  words  (each  of  5  letters)  per 
minute  respectively? 


O  O  OO    CO    O  O    O    OOOO  OOOO   OO 
O    O      O         OO    OO      OO        OO 

OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 

OOO      O     O  OOOOO  OO  O  OOOO    OOO    O  O 
OOO  OOOOO  O      OOO 

O  OO    OO     O  O  OOO 


3.  The  rheostats  of  the  telautograph  are  not  of  the  same  width 
from  one  end  to  the  other,  but  have  a  width  that  is  calculated  to 
compensate  for  the  variation  of  the  line  resistance  occasioned  by  the 
inclusion  of  more  or  less  of  the  resistance  of  these  rheostats.     Formu- 
late an  equation  giving  the  resistance  from  one  end  to  any  point 
on  the  rheostat  so  that  the  line  current  will  be  strictly  proportional 
to  the  distance  of  that  point  from  the  reference  end. 

4.  The  resistances  of  a  selenium  cell  are  30,000  and  20,000  ohms 
under  illuminations  of  20  and  100  luces  intensity.     Calculate  its 
resistance  under  an  illumination  of  i  lux. 

5.  With  the  aid  of  Fig.  17  describe  the  operation  of  the  instru- 
ments for  repeating  from  a  closed-circuit  to  an  induction  telegraph 
line,  and  vice  versa. 


CHAPTER  VII 

MUNICIPAL  TELEGRAPHS 

i .  Fire-alarm  Telegraphy.  —  Signalling  systems  are  in- 
stalled in  cities  and  towns  to  enable  the  inhabitants  to 
notify  the  fire-fighting  force  promptly  of  the  discovery  and 
location  of  a  fire.  The  facts  that  a  fire  in  its  incipiency  is 
more  readily  subdued  than  after  it  has  made  considerable 
headway,  and  that  the  loss  of  human  life  and  property  is 
always  imminent,  render  it  imperative  that  the  fire-fighting 
force  reach  the  scene  of  the  fire  and  begin  its  activities  in 
the  shortest  possible  time.  Fire-alarm  telegraph  systems 
should  have  street  signalling  stations  or  fire-alarm  signal 
boxes  at  convenient  points  throughout  the  territory  served 
that  are  capable  of  being  operated  by  any  one  when  an 
occasion  demands.  In  villages  and  towns  where  the 
fire-fighting  force  is  composed  of  volunteers,  the  operation 
of  a  signal  box  sounds  a  public  alarm  which  indicates  the 
location  of  the  signal  box  operated,  and  the  volunteers 
hasten  to  their  quarters  for  the  fire  apparatus  and  then 
proceed  therewith  to  the  fire.  In  cities  maintaining  paid 
fire  departments,  the  operation  of  a  signal  box  sends  a 
distinctive  signal  to  a  central  station  which  is  equipped 
with  facilities  for  disseminating  this  information  to  the 
firemen  stationed  at  the  apparatus  houses  of  the  fire  depart- 
ment. 

The  time  interval  between  the  discovery  of  a  fire  by 
an  individual  and  the  arrival  of  the  firemen  at  a  fire  in  a 

189 


IQO  TELEGRAPH  ENGINEERING 

city  may  be  divided  into  three  periods.  First,  the  time 
required  for  the  individual  to  reach  the  nearest  street 
signal  box  after  his  discovery  of  fire;  second,  the  time 
taken  between  the  sending  of  the  signal,  usually  called 
"  turning  in  the  alarm  "  or  "  pulling  the  box,"  and  the 
repeating  of  this  signal  in  the  apparatus  houses  of  the  fire 
department;  and,  third,  the  time  elapsing  from  the  recep- 
tion of  the  signal  at  apparatus  houses  to  the  arrival  at 
the  scene  of  the  fire  of  those  fire-fighting  companies  that 
are  expected  to  "  turn  out "  or  answer  the  particular 
signal. 

Of  these  periods,  the  first  depends  largely  upon  the  prox- 
imity of  the  nearest  fire-alarm  box;  thus,  in  the  Borough 
of  Manhattan  of  New  York  City  the  distribution  of  boxes 
is  such  that  the  nearest  box  is  anywhere  from  100  to  upward 
of  800  feet  from  a  building,  depending  to  a  certain  extent 
upon  the  nature  of  the  businesses  or  residences  of  the 
various  districts.  This  time  period  is  frequently  reduced 
by  the  use  of  supplementary  or  auxiliary  boxes  installed 
in  buildings  and  leased  from  private  concerns,  which  are 
designed  when  operated  to  trip  automatically  the  nearest 
street  fire-alarm  box,  and  also  by  the  use  of  thermostatic 
devices  located  in  buildings  and  operated  by  the  fire  itself 
to  send  signals  to  the  office  of  the  company  giving  the 
service,  from  which  point  the  alarm  is  telegraphically 
transmitted  to  the  central  station.  The  second  time  period 
comes  within  the  province  of  municipal  fire-alarm  tele- 
graphs, and  depends  upon  the  signalling  speed  of  the  fire- 
alarm  boxes,  of  central  station  repeating,  and  of  the 
signal-receiving  devices  at  apparatus  houses.  Alarm  trans- 
mission in  New  York  City  requires,  on  the  average,  some- 
what less  than  50  seconds  from  the  pulling  of  the  box  to  the 


MUNICIPAL  TELEGRAPHS  IQI 

last  stroke  of  the  gong  at  apparatus  houses.  The  third 
time  period  depends  upon  the  rapidity  with  which  the 
apparatus  is  turned  out,  its  speed  in  advancing  to  the 
fire  and  the  distance  it  must  traverse.  The  increasing 
use  of  motor-propelled  fire-fighting  apparatus  within  recent 
years  has  materially  diminished  the  duration  of  this  time 
period. 

It  is  apparent  that  the  fire-alarm  boxes  of  a  municipal 
fire-alarm  telegraph  system  might  be  individually  con- 
nected to  the  central  station  by  electric  circuits,  each  ter- 
minating in  an  annunciator  drop  which  bears  the  number 
of  the  box  associated  with  it,  and  that  the  signalling  de- 
vices at  the  apparatus  houses  might  also  be  connected  to 
the  central  station  by  separate  circuits,  thereby  enabling 
operators  to  signal  particular  fire  companies  that  a  fire 
exists  within  their  districts.  The  great  cost  of  a  large 
number  of  such  diverging  circuits  located  on  poles  or  in 
underground  conduits  renders  such  a  system  prohibitive. 
Instead,  in  fire-alarm  systems,  a  number  of  signal  boxes 
are  connected  in  series  on  one  circuit,  and  similarly  the 
signalling  devices  at  a  number  of  apparatus  houses  are 
connected  to  one  circuit;  in  small  municipalities  both 
types  of  devices  are  frequently  joined  to  a  single  circuit. 
In  Manhattan  there  are  approximately  40  box  circuits 
averaging  26  fire-signal  boxes  per  circuit.  While  such 
series-circuit  systems  introduce  more  elaborate  fire-alarm 
boxes,  in  that  each  must  send  a  distinctive  signal  and  should 
be  immune  from  interference  by  the  simultaneous .  actua- 
tion of  other  boxes  on  the  same  circuit,  the  reduction  of 
the  cost  of  line  material  and  its  installation  renders  such 
systems  far  more  economical  than  the  individual-circuit 
arrangement  mentioned  above. 


IQ2  TELEGRAPH  ENGINEERING 

2.  Fire-alarm  Signal  Boxes.  —  The  fire-alarm  boxes  that 
are  distributed  throughout  a  city  are  usually  mounted 
on  posts  located  near  the  curb  of  sidewalks  so 
as  to  be  conspicuous.  One  style  of  fire-alarm 
post,  with  a  glass  globe  for  illumination  at 
night,  is  shown  in  Fig.  i. 

The  turning  in  of  an  alarm  necessitates 
the  opening  of  key  boxes  in  order  to  expose  the 
"hook,"  the  pulling  of  which  starts  the 
mechanism  for  transmitting  the  alarm.  Some 
key  boxes  have  trap  locks  on  their  outer 
doors,  and  when  a  key  is  inserted  it  cannot 
be  withdrawn  until  released  by  a  fire  depart- 
ment officer  with  his  "  release  "  key.  Keys 
to  such  boxes  are  customarily  distributed  to 
responsible  citizens  of  a  town,  each  key  being 
numbered  for  identification.  Other  boxes  have 
keys  permanently  trapped  in  the  locks  and 
covered  with  key  guards  consisting  of  an  iron 
casing  with  a  glass  cover.  Breaking  the  glass 
leaves  the  key  accessible.  With  keyless  boxes, 
a  handle  protrudes  from  the  front  of  the  box, 
as  shown  in  Fig.  i.  In  one  type  of  keyless 
box,  turning  the  handle  opens  the  door  to 
expose  the  hook  for  pulling,  and  also  sounds  a 
local  alarm  on  a  large  gong  within  the  box 
for  attracting  the  attention  of  persons  in  the 
vicinity,  thereby  discouraging  the  sending  of 
false  alarms.  With  the  other  type  of  keyless  box,  the 
turning  of  the  handle  sounds  the  local  alarm  as  well  as 
operates  the  signalling  mechanism  without  opening  the  box. 
Fire-alarm  boxes  are  generally  designed  to  operate  on 


MUNICIPAL  TELEGRAPHS  IQ3 

normally-closed  circuits.  Each  signal  box  is  equipped 
with  a  spring-driven  mechanism  which,  when  set  in  motion 
by  pulling  the  hook,  revolves  a  signal  wheel  that  causes 
the  circuit  to  be  opened  a  definite  number  of  times  with 
definite  time  intervals  between,  thereby  transmitting 
to  the  central  station  a  code  signal  indicating  the  number 
and  thus  the  location  of  the  particular  box  operated. 
Two  such  signal  wheels  located  in  different  fire-alarm  boxes 
are  shown  in  Fig.  2  at  A  and  B.  Each  wheel  has  groups 
of  projections,  one  group  representing  units,  another  tens, 
and  so  on,  and  when  it  revolves  the  projections  suc- 

Central  Station 
Signal  Boxes 


Fig.  2. 

cessively  touch  a  contact  spring,  thereby  closing  the  circuit 
which  extends  to  the  receiving  relay  R  situated  at  the 
central  station.  The  normal  position  of  the  two  signal 
wheels  is  indicated  in  the  figure,  one  wheel  having  3  and  5 
projections  and  the  other  2  and  4  projections  in  its  two 
groups.  When  wheel  A  is  set  in  motion,  the  circuit  is 
opened  3  times  and  after  a  pause  is  opened  5  times,  which 
action  causes  the  bell  at  the  central  station  to  strike  3 
times  and  then  5  times,  a  signal  interpreted  as  35.  The 
mechanism  is  arranged  to  rotate  the  signal  wheel  a  certain 
number  of  times,  usually  four,  with  one  depression  of  the 
hook,  consequently  transmitting  4  rounds  of  number  35 
in  a  complete  signal.  The  signal  boxes  are  designed  so 


IQ4  TELEGRAPH   ENGINEERING 

that  the  mechanism  when  once  started  cannot  be  interfered 
with  by  subsequent  pulling  of  the  hook,  thus  guarding 
against  mutilation  of  the  transmitted  signals  by  excited 
persons  who  do  not  heed  the  usual  directions  appearing 
on  the  inner  cover  of  signal  boxes  to  "  pull  the  hook  down 
once  and  let  go." 

With  signal  boxes  connected  in  series  and  having  the 
parts  indicated  in  Fig.  2,  it  is  possible  that  two  boxes  on 
the  same  circuit  might  be  pulled  at  about  the  same  time, 
and  as  both  signal  wheels  would  then  revolve,  the  signal 
transmitted  by  each  would  be  mutilated  by  that  sent  by 
the  other,  and  both  would  be  lost.  Such  interference 
might  arise,  not  only  because  of  the  breaking  out  of  two 
fires  at  almost  the  same  time  in  districts  served  by  one 
circuit,  but  also  because  of  two  individuals  seeing  the  same 
fire  from  different  points  and  turning  in  alarms  from  differ- 
ent signal  boxes.  The  latter  condition  is  often  minimized 
by  interlacing  the  signal-box  circuits,  so  that  alternate 
boxes  in  both  directions  are  joined  to  different  circuits. 
Both  of  these  causes  of  signal  interference,  however,  may 
be  eliminated  by  the  use  of  signal  boxes  arranged  so  that 
a  box  cannot  transmit  its  signal  while  an  alarm,  originating 
at  another  box,  is  being  transmitted  over  the  same  circuit. 
Such  non-interfering  signal  boxes  first  came  into  use  in 
1870  through  the  invention  of  Game  well,  and  have  since 
been  perfected  by  Crane,  Gardiner,  Ruddick  and  others. 

Ruddick,  in  1889,  introduced  features  in  signal  boxes 
whereby,  if  two  boxes  were  pulled  simultaneously,  neither 
would  interfere  with  the  other,  but  both  would  transmit 
their  signals  properly,  one  after  the  other,  or  successively. 
Thus,  if  a  box  is  pulled  while  another  is  transmitting, 
the  mechanism  of  the  -former  would  operate  without 


MUNICIPAL  TELEGRAPHS  1 95 

affecting  the  circuit  until  the  line  is  again  free,  and  then 
this  box  would  automatically  assume  control  of  the  circuit 
and  send  its  signal. 

Fire-alarm  signal  boxes  may,  therefore,  be  grouped  into 
three  types  in  accordance  with  the  foregoing  description, 


Fig.  3. 


namely:  plain  boxes,  which  are  devoid  of  the  non-inter- 
fering and  successive  features,  non-interfering  boxes,  which 
have  not  the  successive  feature,  and  successive  boxes,  which 
are  also  non-interfering.  The  successive  non-interfering 
type  of  fire-alarm  box  represents  the  highest  development 
of  signalling  devices  on  series  fire-alarm  circuits. 

Fig.  3  shows  the  interior  of  the  positive  non-interfering 


196  TELEGRAPH  ENGINEERING 

successive  fire-alarm  signal  box  made  by  the  Gamewell 
Fire  Alarm  Telegraph  Company.  These  boxes  are  pro- 
vided with  a  mechanism  capable  of  giving  16  rounds 
at  one  operation  of  the  starting  device,  a  single-stroke 
bell  for  striking  at  the  box  the  signal  that  is  being  trans- 
mitted, a  signal  key  for  transmitting  code  signals,  a  test 
switch  for  keeping  the  circuit  closed  while  electrical  or 
mechanical  tests  are  being  made  on  the  box,  a  protector 
against  abnormal  currents,  a  lightning  arrester  and  a 
plug  switch  for  including  either  the  signal  key  or  the  signal 
wheel  in  the  circuit  or  for  grounding  the  circuit  at  the  box 
during  tests.  The  outer  dimensions  of  this  signal  box  are 
18  by  13  by  6  inches. 

The  scheme  of  the  mechanism  and  connections  of  a 
Gamewell  successive  signal  box  is  indicated  in  Fig.  4. 
The  line  wires  terminate  at  the  outer  plates  of  the  plug 
switch,  the  inner  plate  being  grounded.  The  electrical 
devices  in  the  box  are  kept  normally  short-circuited  by 
the  contacts  C,  which  are  kept  closed  by  the  door  of  the 
signal  box,  and  by  the  contacts  C",  which  are  kept  closed 
except  when  the  box  is  actuated.  When  contacts  C'  or 
C"  are  open,  the  line  circuit  includes  the  rear  key  contact, 
the  bell  magnet,  the  "succession"  magnet,  and  the  signal 
contacts  C.  The  opening  and  closing  of  the  signal  con- 
tacts is  under  the  control  of  signal  lever  L,  pivoted  at  h, 
which  carries  a  small  roller  R  for  riding  over  the  teeth  of 
signal  wheel  W.  The  movements  of  lever  L  are  limited 
by  the  actions  of  locking  lever  B,  pivoted  at  e,  by  catch  T, 
pivoted  at  a,  and  by  controlling  lever  £,  pivoted  at  d. 
Signal  wheel  W  and  gear  wheel  G  are  mounted  on  the  same 
shaft  and  are  driven  by  the  main  driving  wheel  D  under 
the  influence  of  the  spiral  spring  S,  the  signal  wheel  mak- 


MUNICIPAL  TELEGRAPHS 


IQ7 


ing  8  revolutions  during  one  revolution  of  the  driving  wheel, 

at  a  speed  governed  by  an  escapement  and  fan,  not  shown. 

When  the  mechanism  is  at  rest,  the  driving  wheel  is 

locked  by  pawl  P,  which  is  attached  to  lever  B,  because 


Fig.  4. 


the  pawl  rests  in  slot  p  or  p'  of  the  upwardly-extending 
flange  of  driving  wheel  D.  When  the  hook  H  is  pulled,  the 
locking  lever  B  is  raised,  carrying  with  it  insulating  block 
/,  thereby  opening  contacts  C".  At  the  same  time  the 
pawl  is  raised  out  of  slot  p  and  the  mechanism  is  set  in 


1 98  TELEGRAPH  ENGINEERING 

motion,  the  pawl  then  slides  over  the  periphery  of  the 
flange  on  D.  Signal  lever  L  does  not  fall  immediately, 
because  it  is  momentarily  held  by  pin  b  or  b'  carried  on  the 
driving  wheel.  If  during  this  short  test  interval  the  line 
circuit  is  uninterrupted,  a  current  will  flow  through  the 
succession  magnet  and  its  armature  A  will  be  attracted, 
consequently  keeping  locking  pin  /  to  the  left  and  clear  of 
signal  lever  L.  As  pin  b  passes  the  downwardly-projecting 
hook  of  the  signal  lever,  this  lever  will  fall  and  the  roller 
R  will  engage  the  teeth  of  the  signal  wheel,  since  catch  T  is 
pushed  to  the  left  when  the  first  tooth  on  the  signal  wheel 
reaches  roller  7?,  and  is  kept  in  this  position  until  the  com- 
plete signal  is  transmitted  by  means  of  the  notched  wheel 
beneath  W  and,  for  a  time  during  each  revolution,  by  lever 
L  itself.  While  the  signal  lever  is  in  its  lower  position, 
pin  /  banks  against  its  left  end  in  order  to  keep  lever  E 
clear  of  the  signal  lever  during  the  intervals  when  the  line 
circuit  is  opened  at  C  and  the  succession  magnet  is  de- 
prived of  current.  After  the  signal  wheel  has  revolved 
four  times  slot  p'  will  be  in  position  for  pawl  P  to  fall  into 
it,  which  action  arrests  the  motion  of  the  mechanism. 
The  engagement  of  pin  b'  with  the  right-hand  end  of  the 
signal  lever  raises  roller  R  from  the  signal  wheel  and  causes 
the  contacts  C  to  be  closed. 

If,  when  the  signal  box  is  pulled,  another  is  transmitting 
its  signal  over  the  same  line,  the  succession  magnet  will  be 
deprived  of  current  at  some  instant  during  the  brief  period 
that  the  signal  lever  is  held  up  by  pin  b  or  bf,  and  conse- 
quently, spring  ^  is  enabled  to  pull  lever  E  away  from  the 
magnet.  Locking  pin  I  then  prevents  the  signal  lever 
from  bearing  on  W,  and  causes  contacts  C  to  be  kept 
closed.  As  the  normal  line  current,  when  traversing  the 


MUNICIPAL  TELEGRAPHS  199 

succession  magnet,  is  not  sufficiently  strong  to  enable  this 
magnet  to  attract  its  armature  when  retracted  to  the  full 
extent,  contacts  C  will  be  kept  closed.  Restoring  pin  r 
bears  against  the  shoe  at  the  lower  end  of  lever  E  once  in 
each  revolution  of  the  signal  wheel,  and  moves  this  lever 
clockwise  so  as  to  bring  armature  A  close  to  the  magnet. 
This  movement,  which  carries  pin  /  clear  of  the  signal  lever, 
does  not  cause  this  lever  to  drop,  because  catch  T  has 
moved  to  the  right  during  this  interval,  since  its  lip  has  been 
pressed  into  the  recess  of  the  notched  wheel  beneath  the 
signal  wheel  W.  After  4  revolutions  of  the  signal  wheel 
the  pawl  P  will  drop  into  the  slot  of  the  flange  on  Z>,  but 
only  partially,  because  the  downward  movement  of  lever 
B  is  checked  by  pin  q  striking  the  shoulder  m.  In  conse- 
quence, the  pawl  is  forced  out  of  this  slot,  and  the  mecha- 
nism continues  in  operation.  At  the  next  instant  lever  E 
is  moved  by  the  restoring  pin  r  so  as  to  bring  armature  A 
close  to  the  magnet.  If,  while  the  armature  is  in  this 
position,  it  is  kept  attracted  by  the  magnet,  the  signal 
lever  will  fall  after  engaging  pin  b  or  b',  and  roller  R  will 
ride  on  the  signal  wheel.  The  box  now  has  control  of  the 
circuit,  and  will  transmit  the  box  number.  But  if,  while 
the  armature  was  close  to  the  magnet,  it  was  not  kept  at- 
tracted, lever  E  would  be  pulled  back  by  spring  s,  and  the 
signal  key  would  be  kept  up  by  the  locking  pin  /.  Thus, 
the  box  " looks  in"  on  the  circuit  every  little  while,  and 
if  it  finds  the  circuit  idle  it  assumes  control  of  the  circuit. 
Should  the  circuit  still  be  open  after  the  signal  wheel  has 
revolved  16  or  20  times,  the  mechanism  is  automatically 
stopped  by  a  ratchet-lever  (not  shown)  and  the  box  number 
will  not  be  transmitted. 
The  appearance  of  the  non-interfering  successive  signal 


2OO 


TELEGRAPH  ENGINEERING 


box  made  by  the  Star  Electric  Company  is  shown  in  Fig:  5. 
This  box  is  equipped  with  a  mechanism  capable  of  repeat- 
ing its  signal  number  forty  times  with  one  winding  of  the 
spring,  a  single-stroke  bell,  a  signal  key,  a  test  switch  for 
testing  the  operation  of  the  mechanism  by  the  response 
of  the  bell  without  sending  any  signals  to  the  receiving 


devices  on  the  box  circuit,  a  protector  against  abnormal 
currents,  a  lightning  arrester  and  a  grounding  switch. 

Fire-alarm  boxes  that  are  wound  by  the  act  of  pulling 
the  starting  lever,  termed  sector  boxes,  are  also  used,  the 
mechanisms  being  driven  either  by  springs  or  weights. 

3.  Public  Alarms.  —  In  villages  or  towns  having  volun- 
teer fire  brigades,  the  volunteers  are  called  by  the  sounding 
of  a  public  alarm  which  is  operated  by  electromechani- 
cal devices  connected  in  the  same  circuit  as  the  signal 
boxes.  Fig.  6  shows  a  Game  well  electromechanical  whistle- 


MUNICIPAL  TELEGRAPHS 


201 


4 


Fig.  6. 


Fig.  7. 


202  TELEGRAPH   ENGINEERING 

blowing  machine  with  a  two-bell  steam  gong.  This  type 
of  public  alarm  gives  satisfactory  results  where  a  steam 
pressure  of  80  pounds  per  square  inch  is  maintained. 
The  weight-driven  mechanism  opens  the  whistle  valve 
simultaneously  with  the  circuit  openings,  and  returns  to 
its  normal  position  every  time  the  circuit  is  closed,  thus 
rendering  the  signal  blasts  sharp,  and  distinct.  Com- 
pressed air  is  also  used  for  blowing  horn  alarms,  the  oper- 
ation being  effected  in  the  same  way  as  with  steam  gongs. 
Electric  horns  are  now  being  introduced  for  public  fire 
alarms. 

Bells  are  frequently  used  for  sounding  public  alarms  in 
cases  of  fire.  A  bell  with  its  electrically-controlled  strik- 
ing mechanism  is  illustrated  in  Fig.  7.  Bell-striking  and 
whistle-blowing  machines  may  be  wound  up  manually 
or  by  automatic  motor-driven  machines  called  electrolifts. 

4.  Fire-alarm  Central  Stations.  —  The  central  stations 
of  fire-alarm  telegraph  systems  comprise  apparatus  for 
receiving,  recording,  and  transmitting  signals  and  fire 
alarms,  which  devices  may  be  designed  for  manual,  semi- 
automatic or  automatic  operation.  Manually-operated 
stations  are  frequently  equipped  also  with  facilities  for 
semi-automatic  and  automatic  transmission  of  signals. 
The  gravity  or  storage  battery  for  operating  all  the  cir- 
cuits of  the  system  is  located  at  the  central  office.  The 
size  and  character  of  fire  central-station  equipments  for 
cities  and  towns  naturally  depend  upon  local  conditions 
and  upon  the  scope  of  the  fire- signalling  system.  Typical 
installations  for  central  stations  will  now  be  considered. 

At  a  manual  central  station,  each  signal-box  circuit  ter- 
minates in  a  visual  drop  and  a  relay;  the  latter  actuates 


MUNICIPAL  TELEGRAPHS  203 

a  bell  and  one  pen  of  a  multiple-pen  register,  Fig.  2.  In- 
coming alarms  are  received  by  one  or  more  operators, 
who  are  on  duty  at  all  times.  Having  heard  the  bell 
signal  and  seen  the  record  on  the  register  tape,  an  operator 
proceeds  to  transmit  the  alarm  to  the  apparatus  houses. 
As  the  receiving  instruments  at  these  houses  are  usually 


Fig.  8. 

grouped  on  several  circuits,  it  is  necessary  to  transmit 
the  signal  over  all  apparatus-house  circuits  simultaneously. 
This  is  accomplished  by  fire-alarm  transmitters,  three 
types  of  which  are  illustrated  in  Figs.  8,  9  and  10. 

Fig.  8  represents  a  spring-driven  detachable  signal- 
wheel  transmitter  with  signal  wheels  that  are  cut  to  cor- 
respond with  those  in  all  the  fire-alarm  boxes  of  the  system. 
These  wheels  are  orderly  arranged  on  pegs  as  shown,  or, 


204  TELEGRAPH    ENGINEERING 

if  numerous,  are  placed  in  accessible  drawers.  Upon 
receiving  an  alarm,  the  proper  signal  wheel  is  selected 
and  placed  in  position  on  the  mechanism,  and  then  the 
handle  is  drawn  to  start  the  mechanism  and  transmit  the 
signal. 

Fig.  9  shows  a  Gamewell  one-dial  four-number  adjus- 


Fig.  9. 

table-speed  weight-driven  transmitter.  The  box  number 
to  be  transmitted  is  set  on  the  dial  at  the  front  by  moving 
the  four  slotted  disks  relative  to  each  other.  The  number 
of  rounds  transmitted  may  be  varied  by  drawing  a  lever 
toward  the  right  to  the  positions  marked  i,  2,  3  or  4. 
This  movement  causes  the  multiple  contacts  at  the  rear 


MUNICIPAL  TELEGRAPHS  205 

to  be  opened  the  proper  number  of  times  and  at  the  correct 
intervals,  thereby  transmitting  the  box  number  simul- 
taneously over  all  the  apparatus-house  circuits. 

The  Star  Electric  Company's  one-dial  four-number 
transmitter  is  illustrated  in  Fig.  10.  Each  digit  is  set  by 
moving  a  lever  down  to  the  desired  number,  and  the  num- 
ber is  then  displayed  near  the  top  of  the  instrument. 


Fig.  10. 

These  transmitters  may  be  equipped  with  speed-changing 
devices  so  that  one  or  more  rounds  of  signals  may  be 
transmitted  over  one  class  of  circuits  at  a  certain  speed 
and  then,  by  an  automatic  shifting  of  the  mechanism,  the 
remaining  rounds  of  the  signals  may  be  transmitted  over 
another  class  of  circuits  at  a  different  speed. 

Some  circuits  extending  to  the  apparatus  houses  also 
have  a  key  and  a  relay  at  their  central  station  ends,  the 


206 


TELEGRAPH   ENGINEERING 


relay  with  a  local  bell  enabling  the  reception  of  signals 
originating  at  the  apparatus  houses. 

Automatic  central  stations  are  used  principally  where  a 
fire-alarm  system  requires  two  or  more  circuits  but  is  not 
large  enough  to  warrant  the  attendance  of  operators. 
Automatic  repeaters  are  used  in  such  stations  for  repeating 
signals  that  come  in  on  any  one  circuit  over  all  the  other 
circuits.  These  repeaters  should  possess  non-interfering 
features  in  order  to  avoid  confusion  of  signals  transmitted 
by  two  or  more  boxes  located  on  different  circuits  when 
pulled  at  the  same  time.  Such  non-interfering  repeaters 


Fig.  zi. 

have  been  devised  by  Skelton,  Kirnan,  Cole  and  others. 
Fig.  ii  shows  an  8-circuit  automatic  repeater  made  by  the 
Gamewell  Fire  Alarm  Telegraph  Co. 

The  operation  of  a  Gamewell  repeater  will  be  under- 
stood by  a  consideration  of  Fig.  12,  which  shows  the  re- 
peating arrangement  and  one  box-circuit  magnet  with 
auxiliary  devices  in  the  normal  condition.  The  weight- 
driven  transmitting  cylinder  D  is  mounted  eccentrically 


MUNICIPAL  TELEGRAPHS 


207 


on  shaft  S  so  as  to  move  contact  rollers  R  and  R'  against 
or  away  from  their  respective  contact  springs  in  the  proc- 
ess of  repeating  alarms  over  box  and  gong  circuits  other 
than  that  over  which  an  alarm  is  being  transmitted.  As 


Fig.  12. 

many  contacts  may  be  provided  as  there  are  gong  and 
signal-box  circuits  in  the  fire-alarm  telegraph  system. 
The  transmitting  cylinder  makes  one  complete  revolution 
every  time  a  box  circuit  is  opened.  Shafts  E,  F,  G1  P  and 
Q  extend  to  the  right  in  front  of  other  repeater  magnets, 
and  carry  levers  before  each  magnet  precisely  as  illustrated 
for  the  one  box-circuit  magnet. 


208  TELEGRAPH   ENGINEERING 

When  the  current  through  magnet  M  is  interrupted, 
armature  A  is  drawn  back  by  spring  s,  carrying  lever  B 
back  with  it.  This  movement  of  B  raises  lever  L  and  with- 
draws pin  p  from  the  path  of  detent  K,  which  is  rigidly 
attached  to  shaft  S.  As  a  result,  cylinder  D  with  its  cams 
C,  Cf  and  C"  is  set  in  rotation.  Gam  C  then  acts  upon 
roller  r  to  depress  lever  L,  thereby  restoring  armature  A 
and  resetting  pin  p  to  obstruct  detent  K  at  the  end  of  its 
revolution.  Cam  C'  depresses  lever  T,  which  through  shaft 
F  and  spring  b  lowers  locking  lever  /  so  as  to  engage  and 
hold  armature  A  against  the  action  of  spring  s  while  no 
current  traverses  the  electromagnet.  Cam  C"  slowly  lowers 
the  right-hand  end  of  lever  N,  and  as  the  opening  o 
reaches  tip  /  of  detent  K' ',  this  tip  is  forced  through  the 
opening  by  clockwork.  Shaft  G  makes  only  a  half  revolu- 
tion because  tip  t' ',  when  it  reaches  its  upper  position,  is 
held  against  the  face  /  of  lever  N.  After  roller  r'  of  lever 
N  reaches  its  highest  position  it  is  gradually  lowered  by 
clockwork  to  its  normal  position,  in  the  process  of  which 
tip  /'  escapes  through  opening  0,  thus  permitting  another 
half  revolution  of  shaft  G.  A  series  of  latches  #,  one  for 
each  repeater  magnet,  is  mounted  loosely  on  eccentrics  on 
shaft  Gj  so  that  the  first  half  revolution  of  this  shaft 
lowers  the  latch,  and  the  second  half  revolution  restores 
it.  With  those  magnets  whose  armatures  are  kept  at- 
tracted because  of  the  normal  current  traversing  them,  the 
downward  movements  of  latches  H  cause  locking  levers 
I  to. move  down  and  hold  the  armatures,  and  also  effect 
the  opening  of  contacts  c  by  means  of  the  pins  pf.  But 
with  the  electromagnet  of  the  box-circuit  over  which  a 
signal  is  being  transmitted,  the  latch  H  was  pushed  back 
by  the  outward  movement  of  the  armature  so  that  its 


MUNICIPAL  TELEGRAPHS  2OQ 

downward  movement  does  not  affect  the  corresponding 
contacts  c.  This  latch  H  is  kept  back  by  pin  p"  on  H 
engaging  with  latch  H'  during  the  further  excursions  of  the 
signalling  armature.  Every  time  the  circuit  is  closed  at 
the  signal  box  the  armature  is  drawn  up  close  to  the  cores 
of  the  electromagnet,  thereby  releasing  the  locking  lever 
by  the  overbalancing  effect  of  weight  W.  When  signalling 
ceases  all  devices  are  automatically  restored  to  the  normal 
position.  A  break  in  any  circuit  will  cause  that  circuit  to 
be  automatically  locked  out  by  the  locking  lever  until  the 
disabled  circuit  has  been  repaired.  The  circuit  on  which  a 
signal  originates  is  indicated  at  the  repeater  by  the  drop  /, 
which  is  thrown  back  by  the  armature  when  the  circuit  is 
first  opened.  All  alarms  transmitted  by  the  repeater  are 
usually  recorded  on  a  register. 

With  systems  arranged  for  semi-automatic  operation, 
incoming  signals  are  received  and  recorded  at  the  central 
station,  but  after  one  round  of  a  box  number  has  been 
signalled,  the  operator  may  cause  the  remaining  rounds  to 
be  transmitted  directly  to  the  apparatus  houses  of  the  fire 
department. 

The  signal-box  and  apparatus-house  circuits  of  a  fire- 
alarm  telegraph  system  generally  terminate  at  a  switch- 
board in  the  central  station,  upon  which  is  located  the 
various  devices  associated  with  these  circuits.  Where 
storage  batteries  are  used  for  operating  the  circuits,  a  bat- 
tery switchboard  is  installed  for  enabling  the  charging  of 
the  cells  in  series,  multiple,  or  series-multiple  as  may  be 
necessary,  for  switching  from  one  battery  to  a  reserve 
battery,  and  for  testing  purposes.  Such  a  switchboard 
is  shown  in  Fig.  10,  located  behind  the  fire-alarm 
transmitter. 


2IO 


TELEGRAPH   ENGINEERING 


5-  Signalling  Devices  at  Apparatus  Houses.  —  In  fire- 
alarm  signalling  systems  having  automatic  central  stations 
or  having  manual  stations  employing  a  single  method  in 

transmitting  alarms,  the  sig- 
nalling equipment  at  apparatus 
houses  comprises  electrome- 
chanical gongs  and  frequently 
registers  or  visual  alarm  indica- 
tors. The  gongs  have  spring- 
driven  mechanisms  and  strike 
one  blow  every  time  the  circuit 
is  closed.  The  usual  sizes  of 
gongs  are  6,  8,  9,  10,  12,  15  and 
1 8  inches  in  diameter.  The 
indicators  are  spring-driven 
electromechanical  devices  for 
displaying  the  box  numbers  in 
large  figures,  being  operated 
only  by  the  first  round  of 
signals.  Such  indicators  are 
designed  for  showing  either 
three  or  four  digits,  each  digit 
being  brought  into  view  by  a 
wheel  bearing  the  numbers 
from  i  to  9  on  its  periphery. 
The  mechanism  is  of  the  step- 
by-step  type,  and  is  manually 
restored  by  the  pulling  of  a 

cord.  Both  gong  and  indicator  may  be  combined  into  one 
instrument  as  shown  in  Fig.  13,  which  depicts  a  1 5-inch 
electromechanical  gong  with  a  three-digit  indicator. 

Registers  yield  a  record  of  received  alarms  either  by 


Fig.  13. 


MUNICIPAL  TELEGRAPHS  211 

ink  marks  or  perforations  in  paper  tapes.  Fig.  14  shows 
a  punching  register,  paper  take-up  reel  and  an  automatic 
time  and  date  stamp  which  prints  on  the  register  tape  the 
exact  time  that  alarms  are  received. 

With  systems  having  manual  central  stations  and  em- 
ploying two  different  methods  in  transmitting  alarms  to 
apparatus  houses,  two  circuits  enter  each  of  these  houses 
from  the  central  station,  and  these  are  called  "  gong  cir- 


Fig.  14. 


cuits  "  and  "  joker  circuits."  The  gong  circuits  terminate 
at  apparatus  houses  in  electromechanical  gongs  and  some- 
times also  in  indicators,  as  described  above.  The  joker 
circuits  terminate  in  single-stroke  electric  bells,  or  tappers, 
having  5-  or  6-inch  gongs,  and  also  frequently  in  registers. 
With  such  systems  one  or  more  rounds  of  signals  may  be 
transmitted  at  high  speed  over  the  joker  circuits  and  then 
the  remaining  rounds  transmitted  over  the  gong  circuits 
at  the  necessarily  slower  speed  suitable  for  electromechan- 
ical gongs,  or  vice  versa. 

Where  routine  telegraphic  communication  is  desirable 
between  the  central  office  and  the  apparatus  houses,  joker 
circuits  are  also  equipped  with  relays,  -sounders  and  keys 
at  all  stations.  These  circuits  may  be  used  for  routine 
instructions  and  messages  when  no  alarms  are  being  trans- 


212 


TELEGRAPH  ENGINEERING 


mitted,  but  as  soon  as  alarm  transmission  commences, 
telegraphic  communication  ceases.  Such  circuits,  enabling 
both  telegraphic  and  alarm  signalling,  are  called  combina- 
tion circuits.  A  scheme  of  connections  of  a  signal  equip- 
ment at  apparatus  houses  for  use  on  gong  and  combination 
circuits  is  represented  in  Fig.  15,  the  gong  circuits  being 
normally  open  and  the  combination  circuit  normally 
closed.  Relay  armature  a,  controlling  the  telegraphic 


Gong  Circuit 


Sounder 


Fig.  15- 


apparatus,  is  attracted  when  the  small  normal  currents 
traverse  the  combination  circuit,  but  armature  b,  con- 
trolling the  tapper,  is  attracted  only  when  a  larger  current 
is  sent  out  on  the  line,  which  function  is  performed  by 
the  central  station  transmitter  in  the  process  of  trans- 
mitting alarms. 

6.  Operation  and  Routine  of  a  Fire-alarm  Telegraph 
System.  —  The  operation  of  municipal  fire  departments 
in  receiving  and  responding  to  alarms  is  obviously  different 
in  the  various  cities.  A  particular  fire  department,  that 
of  Brooklyn,  N.  Y.,  which  serves  a  population  of  1,800,000 
inhabitants  and  protects  an  area  of  71  square  miles,  will 
here  be  considered. 


.       MUNICIPAL  TELEGRAPHS  213 

There  are  1800  fire-alarm  boxes  included  in  40  circuits 
which  lead  to  the  manual  central  station  on  Jay  St.,  and 
there  are  4  combination  and  7  gong  circuits  extending 
from  this  central  station  to  the  91  apparatus  houses  of  the 
department.  Each  box  circuit  terminates  at  the  central 
office  in  a  relay,  which  controls  one  pen  of  a  3o-pen  register 
and  a  tapper.  Each  of  these  box  circuits  passes  through 
one  or  more  apparatus  houses  for  affording  convenient 
places  for  line  testing.  Two  rounds  of  an  alarm  are  trans- 
mitted over  the  gong  circuits  by  means  of  a  four-dial 
four-number  transmitter,  and  then  two  rounds  are  trans- 
mitted manually  over  the  combination  circuits  by  means 
of  a  multiple  key.  A  three-position  telephone  switch- 
board at  the  central  station  is  connected  to  the  "  Main  " 
exchange  of  the  New  York  Telephone  Company  through 
10  trunk  lines,  for  receiving  calls  for  fire-fighting  apparatus 
by  telephone.  Each  apparatus  house  is  joined  to  this 
private  branch  telephone  switchboard  by  a  direct  or  a 
party  line. 

An  area  of  4.8  square  miles  of  Brooklyn  is  protected  by 
high-pressure  service,  supplied  by  two  pumping  stations. 
Alarms  of  fire  are  received  at  these  stations  simultaneously 
with  the  apparatus  houses  and  a  water  pressure  of  75 
pounds  per  square  inch  is  immediately  applied  to  the  water 
mains.  There  are  215  telephone  boxes  connected  directly 
with  the  pumping  stations  for  enabling  fire  department 
officers  to  call  for  increased  pressure  or  order  the  system 
shut  down. 

The  duties  of  fire  companies  and  officers  are  largely 
directed  by  an  assignment  book.  Upon  the  pulling  of  a 
box  (or  sending  a  first  alarm)  and  the  subsequent  receipt 
of  the  number  of  that  box  at  the  apparatus  houses,  certain 


214  TELEGRAPH  ENGINEERING 

engine  companies,  hook  and  ladder  companies,  and  chiefs 
immediately  respond  to  the  alarm.  Upon  the  receipt 
of  a  second,  third  and  fourth  alarms  from  the  same  signal 
box,  other  companies  respond  without  other  notification 
than  the  receipt  of  the  particular  alarm,  and  further, 
still  other  companies  move  from  their  own  quarters  into 
those  made  vacant  by  companies  responding  to  earlier 
alarms.  If  more  apparatus  is  needed  than  available  on 
the  fourth  alarm,  special  calls  are  made  by  the  central 
station  operator.  Such  calls  are  also  made  in  order  to 
supply  a  substitute  for  any  company  that  for  various 
reasons  may  be  prevented  from  answering  an  alarm  sent 
from  a  box  to  which  that  company  is  regularly  assigned. 
The  operator  must,  therefore,  be  kept  constantly  informed 
upon  the  preparedness  of  all  companies  and  officers  to 
respond  to  immediate'  call. 

To  illustrate  the  use  of  this  method  of  answering  alarms 
upon  signal,  consider  that  box  93,  located  at  Borough  Hall, 
be  pulled.  The  location  of  this  signal  box  and  that  of 
the  various  fire  companies  in  this  section  of  Brooklyn  are 
indicated  in  Fig.  16  by  small  circles  bearing  the  proper 
numbers  of  the  companies.  Numbers  between  30  and 
50  represent  battalion  chiefs,  numbers  between  100  and  200 
represent  hook  and  ladder  companies,  numbers  over  200 
represent  engine  companies,  numbers  preceded  by  S  rep- 
resent fire  insurance  salvage  corps,  numbers  10  and  n 
represent  deputy  chiefs,  C  represents  the  chief  of  the  depart- 
ment, 6  represents  a  water  tower,  SI  represents  a  search- 
light engine  and  numbers  preceded  by  FB  represent  fire 
boats.  The  assignments  for  box  93  follow,  the  first  line 
gives  the  numbers  of  the  companies  and  officers  responding 
to  the  first  alarm  from  this  box,  the  second  line  those  for 


MUNICIPAL  TELEGRAPHS 


215 


2l6 


TELEGRAPH   ENGINEERING 


the  second  alarm,  etc.,  the  sequence  of  the  numbers  of  each 
group  being  the  order  in  which  the  companies  are  expected 
to  arrive  at  the  signal  box.  These  assignments  are  also 
shown  in  Fig.  16  by  the  light  dotted  lines  marked  I,  II, 
III  and  IV  which  are  drawn  to  include  the  locations  of  all 
companies  and  officers  that  are  assigned  to  answer  the  first 
second,  third  and  fourth  alarms  respectively  sent  from 
box  93.  The  changes  of  company  locations  on  the  third 
and  fourth  alarms  are  also  indicated. 


Station 

Engine  companies 

Hook 
and 
ladder 
com- 
panies 

Dep- 
uty 
chief 

Bat- 
talion 
chiefs 

Water 
tower 

Companies  to  change 
locations 

Engine 
companies 

H.  &L. 
Go's. 

93 

Joralemon 
and  Court 
Streets 

205,  224,  207 
226,  204,  206,  256    SI 

203,  208,  210 
219,  279,  202 

118,  no 

103 

105 

10 

31,.  33 
32 

34 

119  to  118 

6 

(  209  to  226  ) 
(  251  to  206  J 
(235  to  219  ) 
(239  to  204  ) 

Alarms  beyond  the  first  are  sent  to  the  central  station 
by  officers  of  the  fire  department  or  their  aids  by  trans- 
mitting, with  the  telegraph  key  at  any  signal  box  near  the 
fire,  the  numbers  2,  2  and  the  box  number  for  the  second 
alarm,  or  3,  3  and  the  box  number  for  the  third  alarm,  etc. 
Any  engine  company  may  be  ordered  by  the  central-station 
operator  to  respond  to  a  box  to  which  it  is  not  regularly 
assigned  by  transmitting  over  the  apparatus-house  circuits 
the  number  5,  the  box  number  and  then  the  company 
number  in  close  succession.  Such  special  calls  may  also 
be  made  for  hook  and  ladder  companies  by  transmitting 
the  number  7,  the  box  number  and  then  the  company 
number.  On  their  return  from  a  fire,  engine  companies 
and  hook  and  ladder  companies  signify  their  preparedness 


MUNICIPAL  TELEGRAPHS 


217 


to  answer  another  call  by  transmitting  respectively  to  the 
central  office  over  the  combination  circuits  the  numbers 
4,  4,  4  and  the  company  number,  and  4,  4,  4,  7  and  the  com- 
pany number,  the  operator  answering  this  signal  by  the 
numbers  2,  3.  Should  a  company  be  called  out  on  a  "  still 
alarm,"  one  of  its  firemen  informs  the  central  operator 
to  this  effect  by  transmitting  2,  2,  2,  the  company  number 
and  then  the  number  of  the  box  nearest  the  scene  of  the  fire. 
In  all  five  boroughs  of  New  York  City  (280  square 
miles)  there  are  13  deputy  chiefs,  43  battalion  chiefs,  181 
engine  companies,  93  hook  and  ladder  companies,  10  fire- 
boats  and  8  hose  companies;  the  personnel  totals  6740 
individuals.  The  number  of  fires  and  false  alarms  and  the 
resulting  loss  to  buildings  and  contents  in  this  city  during 
the  first  nine  months  of  1913  are  given  below;  the  average 
loss  per  fire  during  this  period  is  found  to  be  $542. 


1913 

Number  of 
fires 

Number  of 
false  alarms 

Loss  in  dollars 

Total  (Jan.-Sept.)  

9660 

I2Q3 

"?,2it;,o87 

Average  per  day  

7C 

c 

19,103 

7.  Police  Patrol  Telegraphs.  —  Signalling  systems  are 
installed  in  cities  for  enabling  policemen  to  transmit  code 
signals  for  summoning  assistance,  calling  ambulances  or 
patrol  wagons,  and  informing  headquarters  that  they  are 
on  duty,  and  to  communicate  with  their  superior  officers 
by  telephone.  Such  police-patrol  signal  systems  have 
many  features  in  common  with  fire-alarm  signal  systems, 
already  described.  Means  for  transmitting  signals  from 
headquarters  to  convenient  points  in  the  city,  for  calling 
any  or  all  patrolmen  to  their  nearest  street  stations  for 


2l8  TELEGRAPH   ENGINEERING 

the  purpose  of  receiving  instructions,  may  be  incorporated 
in  police  signal  systems.  In  some  cities  police  signal 
systems  utilize  telephone  instruments  exclusively. 

Police  signal  boxes  resemble  fire-alarm  boxes  in  that 
they  include  a  mechanism  for  transmitting  the  box  number 
by  means  of  a  signal  wheel,  a  telegraph  key  and  a  single- 
stroke  bell.  In  addition,  police  signal  boxes  have  a  tele- 
phone receiver,  a  telephone  transmitter  and  an  induction 


Fig.  17. 

coil,  properly  connected  together  to  form  a  telephone  set. 
Fig.  17  represents  a  Gamewell  y-call  police  signal  box 
with  its  outer  door  open,  and  Fig.  18  shows  the  same  box 
with  both  outer  and  inner  doors  open  to  exhibit  the  various 
parts. 

When  a  policeman  has  occasion  to  send  any  one  of  the 
seven  code  signals,  he  moves  a  pointer  to  the  proper  posi- 
tion as  indicated  by  the  plate  on  the  inner  cover  (Fig.  17) 


MUNICIPAL  TELEGRAPHS 


219 


and  then  pulls  the  crank  located  just  below  the  pointer. 
Thus,  if  the  pointer  of  box  34  is  placed  in  the  second 
position  corresponding  to  "  ambulance,"  the  mechanism 
would  transmit  2  dots  at  slow  speed  followed  after  a  short 
pause  by  the  box  number  3,  4  at  faster  speed.  If  a  patrol- 
man transmits  an  "  on  duty  "  code  signal  and  the  cen- 
tral station  attendant  wishes  to  converse  with  him,  the 


Fig.  18. 

attendant  depresses  a  key  a  prearranged  number  of  times 
immediately  after  receiving  the  code  signal,  which  act 
causes  the  bell  at  the  signal  box  to  sound  accordingly, 
thereby  notifying  the  patrolman  to  use  the  telephone. 

Numbered  keys  may  be  given  to  responsible  citizens 
with  which  they  can  operate  the  police  signal  boxes  when 
in  need  of  police  assistance  without  opening  the  outer  door, 
such  keys  when  used  being  trapped  in  the  locks  for  iden- 
tifying the  possessors. 

Incoming  signals  are  usually  received  at  the  precinct 


220  TELEGRAPH   ENGINEERING 

headquarters  by  a  tapper  and  a  register.  Calls  for  patrol 
wagons  are  transmitted  by  the  operator  to  the  police 
stables  and  garages,  the  number  of  the  signal  box  being 


Fig.  19. 


sent  out  by  detachable  signal-wheel  or  special  dial  trans- 
mitters. The  equipment  at  the  stables  and  garages  usually 
includes  an  electromechanical  gong  and  indicator  as  illus- 


MUNICIPAL   TELEGRAPHS  221 

trated  in  Fig.  13,  a  register  with  take-up  reel  as  indicated 
in  Fig.  14,  a  tapper  and  a  telephone  set.  Upon  the  receipt 
of  a  call  for  a  patrol  wagon  at  these  places,  a  wagon  is 
dispatched  from  the  stable  nearest  the  signal  box  from 
which  the  call  originated. 

Fig.  19  shows  the  Star  Electric  Company's  unit- type 
central-office  police  desk  with  the  necessary  devices  for 
receiving  code  or  telephone  calls  over  box  circuits,  for 
transmitting  calls  for  patrol  wagons  and  ambulances, 
for  calling  one  or  more  patrolmen  on  duty  by  flashlight 
or  bell  signals  to  proceed  to  their  nearest  signal  boxes 
for  receiving  orders,  for  controlling  and  charging  the 
storage  battery  which  supplies  current  to  the  signal  cir- 
cuits, and  for  testing  the  continuity  and  insulation  of 
the  circuits.  This  cabinet  is  arranged  for  3  box  circuits, 
2  flashlight  circuits,  i  chief's  circuit,  i  stable  circuit  and 
i  test  circuit. 

8.  Statistics  of  Police  and  Fire  Signalling  Systems.  - 
The  latest  published  census  statistics  of  fire-alarm  and 
police-patrol  telegraph  systems  in  the  United  States  are 
for  the  year  1907.  The  following  table  gives  data  selected 
from  this  census  on  signalling  systems  used  for  fire  alarms 
exclusively,  those  used  jointly  for  fire  alarm  and  police 
signal  service,  and  those  used  for  police  patrol  signalling 
exclusively,  the  various  systems  being  grouped  according 
to  population  of  the  cities  wherein  installed. 

Of  the  38  cities  with  a  population  in  excess  of  100,000, 
there  are  28  +  8  or  36  having  fire-alarm  systems;  the  re- 
maining 2  cities,  Kansas  City  and  St.  Joseph,  Mo.  depended 
entirely  upon  the  telephone  for  transmitting  alarms  of  fire. 
Of  the  40  cities  having  from  50,000  to  100,000  inhabitants, 


222 


TELEGRAPH  ENGINEERING 


39  have  fire-alarm  systems  and  Kansas  City,  Kans.  de- 
pended upon  telephonic  fire-alarm  transmission.  The  cities 
of  Quincy,  111.  and  Chester  and  Williamsport,  Pa.  of 
36,000,  34,000  and  29,000  inhabitants  respectively,  were 
reported  as  having  no  fire-alarm  systems. 


Fire-alarm  signal  systems 


Cities  having  populations  of 


100,000 

and 
over 

50,000 
to 

100,000 

25,000 
to 
50,000 

10,000 
to 
25,000 

Less 

than 
10,000 

Total 

Number  of  cities  in  group  *  
Fire-alarm  systems  
Fire  alarms  received  in  1907  
Signal  boxes  

38 
28 
39.581 
12,151 

40 
35 
10,700 
4,268 

82 
69 
14,372 
5.387 

281 
231 

17,688 
8,700 

'"568 
14,175 
9,895 

"931 
96,516 
40,401 

Telephone  boxes  
Miles  of  single  wire  

216 
17,218 

3,377 

37 
3,447 

112 

5.322 

131 

5,973 

496 
35.337 

Manual  transmitters  
Automatic  transmitters  

30 

24 

16 
34 

14 
52 

46 
IO3 

58 
73 

164 
286 

Receiving  circuits  
Transmitting  circuits  

584 
332 

265 
182 

368 
196 

712 
366 

880 
394 

2,809 
1,470 

Combined  fire-alarm  and  police-patrol  signal  systems 

Combined  systems  
Fire  alarms  received  in  1907 

8 
19.832 
8,118 
i,9i5 
19,223 
17 
8 
356 
108 

4 
959 
669 
127 
1.  154 

2 

4 
34 
20 

10 
1,848 
93i 

& 
1 

74 

52 

14 

109 
601 
6 
3 
81 
35 

12 
6l9 
338 
10 
156 
2 
I 

27 
13 

48 
24,203 
10,721 
2,192 
21,897 
31 
24 
572 
228 

Signal  boxes  t  
Telephone  boxes 

Miles  of  single  wire  

Automatic  transmitters  

Transmitting  circuits  

Police-patrol  signal  systems 


Police  signal  systems  
Signal  boxes  t 

27 

3,758 

29 

1,204 

39 
1,020 

$ 

& 

178 
6,999 

Telephone  boxes  
Miles  of  single  wire  

1,054 
8,788 

no 
1.543 

153 
1,601 

226 
1,148 

152 

498 

1.695 
13.578 

Transmitters                          

107 

12 

21 

31 

3 

174 

Receiving  circuits  

358 

117 

181 

136 

96 

888 

Transmitting  circuits  

191 

75 

1  20 

76 

29 

491 

*  Population  based  on  1900  census. 

t  Combined  signal  and  telephone  boxes  were  in  most  cases  reported  as  signal  boxes. 


MUNICIPAL  TELEGRAPHS  223 

PROBLEMS 

1.  Explain  that  if  two  successive  fire-alarm  boxes  are  pulled  simul- 
taneously, that  box  whose  number  has  the  lowest  first  digit  will  as- 
sume control  of  the  circuit  before  the  other  signal  box. 

2.  Show  the  scheme  of  connections  at  the  central  office  of  3 
fire-alarm  box  circuits,  each  terminating   in  a  relay  and  a  drop, 
the  relays  controlling  the  operation  of  a  common  tapper  and   a 
3 -pen  register. 

3.  Formulate    the   assignments  of  fire-fighting   companies   and 
officers  for  signal  box  number  234  located  at  Fulton  St.  and  Hudson 
Ave.,  Brooklyn.     The  location  of  this  box  and  of  the  various  com- 
panies and  officers  is  shown  in  Fig.  16,  the  same  number  of  com- 
panies being  assigned  to  this  box  as  to  box  93. 


CHAPTER   VIII 

RAILWAY  SIGNAL  SYSTEMS 

i.  Classes  of  Railway  Signalling.  —  Railway  signals  for 
the  conveyance  of  information  to  those  engaged  in  running 
trains  or  cars  fall  into  the  following  classes:  (a)  block 
signals  which  indicate  whether  or  not  a  train  may  proceed 
into  the  next  track  section  or  block;  (b)  train-order  signals 
for  advising  engineers  when  train-dispatcher's  orders  are 
to  be  given  them;  (c)  route  or  switch  signals  for  authorizing 
the  passage  of  trains  over  junctions,  crossings,  drawbridges, 
etc. ;  (d)  other  signals,  such  as  flags,  lanterns  and  torpedoes, 
for  the  warning  of  temporary  dangers,  and  fixed  signs  for 
indicating  speed  limits,  location  of  water  tanks,  etc. 
Classes  b  and  d  lie  outside  the  scope  of  electric  signalling, 
the  former  class  always  being  manual  signals  operated  by 
the  telegraphers  who  take  the  train  orders. 

Block  signals  are  used  on  lengths  of  track  devoid  of 
switches  and  crossings  for  limiting  the  space  between  two 
trains  on  the  same  track  to  an  amount  affording  a  proper 
braking  distance  for  those  trains  running  over  this  track 
at  maximum  speed.  On  single-track  roads,  block  signals 
also  give  proceed  and  stop  indications  to  trains  advancing 
in  opposite  directions.  Block  signals  may  be  manually 
operated,  manually  controlled,  or  automatic.  Manually- 
operated  block  signals  are  operated  either  by  engine  drivers 
or  motormen  upon  reaching  a  block,  or  by  attendants 
stationed  along  the  roadway  who  set  their  signals  in  accord- 

224 


RAILWAY    SIGNAL   SYSTEMS  225 

ance  with  information  of  train  movements  received  by 
telegraph  or  telephone  from  their  neighboring  attendants. 
Manually-controlled  block  signals  are  set  by  attendants,  the 
action  of  one  in  operating  signals  being  under  the  control 
of  another;  thus,  two  attendants,  one  at  each  end  of  a 
block,  must  act  in  setting  a  signal.  Automatic  block  signals 
are  actuated  by  track  or  trolley  attachments,  or  are  oper- 
ated through  an  electric  track  circuit,  the  train  movements 
governing  the  signals  in  both  cases.  These  arrangements 
control  either  a  local  electric  circuit  which  operates  the 
signal,  or  a  valve  which  allows  compressed  air  or  gas  to 
move  the  signal. 

Route  or  switch  signals  are  the  signals  of  interlocking 
plants  which  comprise  groups  of  switches  and  signals  that 
govern  the  movements  of  trains  at  crossings,  junctions, 
terminal  yards,  etc.  The  switches  and  signals  of  inter- 
locking plants  may  be  moved  manually  or  by  means  of 
compressed  .gas  or  of  electricity  under  the  control  of  lever- 
men,  the  individual  movements  for  establishing  a  track 
route  following  each  other  in  a  predetermined  order.  These 
signals  also  act  in  conjunction  with  the  block  signals  just 
beyond  interlocked  territories. 

2.  Types  of  Signals.  —  Signals  for  block  systems  and 
interlocking  plants  may  be  electric  lights,  semaphores 
(with  lights  as  night  signals),  or  enclosed  disk  signals  (with 
lights  as  night  signals) .  These  signals  indicate  in  different 
ways  the  commands:  Stop  —  danger,  proceed  with  caution, 
and  clear  —  proceed.  With  light  signals,  these  commands 
are  displayed  by  utilizing  a  distinctive  color  for  each :  thus, 
red  is  used  as  the  danger  signal,  green  generally  as  the  clear 
signal,  and  orange-yellow  usually  as  the  caution  signal. 


226 


TELEGRAPH  ENGINEERING 


Semaphores  are  either  of  the  two-position  or  three-posi- 
tion type,  the  blade  positions  for  the  various  indications 
being  shown  in  Fig.  i.  A  high  three-position  semaphore 
is  shown  at  A}  this  signal  being  mounted  on  iron  masts 
placed  beside  the  tracks  or  on  signal  bridges.  A  dwarf 


DANGER 


CAUTION 


\CLEAR 


Fig.  i. 


three-position  signal  is  shown  at  B,  and  is  mounted  directly 
alongside  of  the  tracks,  usually  at  interlocking  plants. 
These  three-position  upper-quadrant  signals  indicate  by 
their  blade  positions:  danger  when  horizontal,  caution 
when  inclined  upward  at  45  degrees,  and  clear  when  vertical. 
Two  two-position  semaphore  signals  mounted  on  the  same 
mast  are  shown  at  C,  the  upper  serving  as  the  home  blade 


RAILWAY   SIGNAL   SYSTEMS  227 

and  the  lower  as  the  advance  or  distant  blade  of  a  block 
signal.  Both  blades  horizontal  signify  "  stop,"  the  upper 
inclined  downward  60  degrees  and  the  lower  horizontal 
mean  "  proceed  with  caution,"  and  both  inclined  down- 
ward 60  degrees  signify  "clear."  Spectacles  carrying  col- 
ored glasses  are  fastened  rigidly  to  the  semaphore  blades  so 
as  to  move  in  front  of  lamps,  thereby  displaying  at  night 
colored  light  signals  corresponding  to  the  blade  positions. 

Enclosed  disk  signals  consist  of  an  electromagnet  whose 
armature  controls  the  position  of  a  wire  hoop  covered  with 
colored  bunting,  all  enclosed  in  a  glass-covered  case.  When 
the  magnet  is  energized,  the  colored  disk  is  drawn  away 
from  the  aperture  and  a  white  background  is  visible;  when 
released,  the  disk  falls  into  position  and  its  color  is  dis- 
played. Colored  glass  disks,  similarly  controlled  and  mov- 
ing before  a  lamp,  serve  as  the  night  signals.  Such  enclosed 
signals,  while  once  widely  used,  are  now  infrequently 
employed. 

Electric  light  signals  assume  a  variety  of  forms  depending 
upon  the  conditions  of  use;  three  styles  made  by  the  Union 
Switch  and  Signal  Company  are  shown  in  Fig.  2.  The 
block  signal  used  by  the  Interborough  Rapid  Transit 
Company  in  the  New  York  Subway  is  shown  at  A.  The 
upper  or  home  signal  displays  either  a  red  or  a  green  light, 
and  the  lower  or  distant  signal  shows  either  a  yellow  or  a 
green  light,  both  being  provided  with  an  auxiliary  miniature 
semaphore  signal  immediately  below  the  lenses  for  use  in 
case  of  lamp  failures.  Colored  glass  disks  supported  in 
vertical  sliding  frames  move  in  front  of  the  lamp  apertures 
by  means  of  compressed  air,  the  valves  being  controlled  by 
electric  track  circuits  (§5).  The  block  signal  used  in  the 
Pennsylvania  Railroad  Tubes  under  the  Hudson  and  East 


228 


TELEGRAPH   ENGINEERING 


Rivers  is  shown  at  B,  the  three  upper  lights  performing  the 
same  function  as  a  three-position  semaphore,  since  only  one 
can  be  illuminated  at  a  time.  The  lower  lamp  always 


Fig.  2. 


remains  lighted  and  serves  as  a  fixed  signal.  Similar 
signals  with  an  additional  lower  lamp  are  used  as  inter- 
locking signals.  At  C  is  shown  a  type  of  signal  for  daylight 
service  used  by  the  Indianapolis,  Columbus  &  Southern 


RAILWAY   SIGNAL  SYSTEMS  22Q 

Traction  Company  and  by  other  electric  railway  com- 
panies. 

Semaphores  for  block  and  interlocking  signals  are  some- 
times distinguished  from  each  other  by  their  color  or  by  the 
shape  of  the  ends  of  their  blades.  The  indications  of  sema- 
phores used  with  automatic  block  signal  systems  may  be 
normally  danger  or  clear.  A  normal  danger  signal  ordi- 
narily stands  at  "  danger,"  but  goes  to  "  clear  "  as  a  train 
approaches  it  if  the  block  governed  by  the  signal  is  clear, 
returning  to  "  danger  "  when  the  train  enters  the  block. 
A  normal  clear  signal  stands  at  "  clear  "  except  when  a 
train  occupies  the  block  governed  by  the  signal.  Normal 
clear  signals  are  now  preferred  by  signal  engineers. 

Mechanical,  electric,  electro-pneumatic  and  electro-gas 
devices  are  used  for  actuating  the  semaphores  and  switches 
of  interlocking  plants,  and  (excepting  the  first),  for  operat- 
ing the  semaphores  of  automatic  block  signal  systems. 
Electric-motor  semaphores  &re  now  more  frequently  in- 
stalled than  semaphores  actuated  in  other  ways. 

The  mechanism  of  the  Style  B  upper-quadrant  two- 
position  direct-current  semaphore,  manufactured  by  the 
Union  Switch  &  Signal  Company,  is  shown  in  Fig.  3.  The 
track  circuit  is  arranged  so  that  the  motor  A  and  the  holding 
magnet  B  receive  current  while  the  block  governed  by  the 
signal  is  being  cleared.  When  the  signal  subsequently 
indicates  "  clear  "  the  motor  is  open-circuited  but  the  flow 
of  current  through  the  holding  magnet  remains  uninter- 
rupted. The  holding  magnet  is  fixed  to  the  "  slot  arm  " 
C  which  rocks  around  pivot  D.  This  slot  arm  carries  the 
rod  E  which  connects  with  the  semaphore  blade,  and  also 
carries  a  system  of  links  terminating  in  the  cam  piece  F 
which  may  engage  the  trunnions  of  the  chain  G.  The 


230 


TELEGRAPH   ENGINEERING 


Fig.  3. 

passing  of  a  train  out  of  the  block  causes  the  operation  of 
the  semaphore  motor,  the  rotation  of  which  produces  an 
upward  movement  of  the  chain  through  the  gear-wheels 
H  and  /.  Simultaneously,  the  armature  of  the  holding 
magnet  is  attracted,  thereby  holding  the  system  of  links 


RAILWAY   SIGNAL  SYSTEMS 


23I 


and  the  cam  F  rigid.  This  cam,  consequently,  engages  a 
trunnion  of  the  upwardly-moving  chain,  and  the  -slot  arm 
is  carried  to  its  upper  position,  corresponding  to  the  clear 
position  of  the  semaphore.  At  this  position,  the  circuit  of 
the  motor  is  automatically  opened  at  /  by  the  slot  arm, 
this  arm  remaining  in  its  upper  position  as  long  as  the 
holding  magnet  is  energized. 

The  presence  of  a  train  in  the  block  causes  the  release  of 
the  holding-magnet  armature  and  the  loosening  of  cam  F, 
this  action  allowing  the  slot  arm  to  descend  by  gravity  to 
the  position  shown  in  the  figure.  The  pneumatic  buffer 
K,  connected  to  the  right-hand  end  of  the  slot  arm,  permits 
the  gradual  return  of  the  semaphore  to  this  danger  position. 
Series-wound  or  induction  alternating-current  motors  may 
also  be  used  with  this  mechanism.  By  the  addition  of 
another  slot  arm,  the  same  motor  may  operate  the  other 
position  for  a  one-blade  three-position  signal  or  the  second 
blade  of  a  two-arm  (home  and  distant)  signal. 

Trolley  Wire 


Signal  Wire 


Fig.  4. 

3.  Manual  Block  Signal  Systems.  —  The  scheme  of  a 
manually-operated  block  signalling  arrangement,  frequently 
used  on  single-track  electric  railways  operating  relatively 
few  cars,  is  shown  in  Fig.  4.  A  signal  box,  having  three 
electric  lights,  L\y  L2  and  Z,3,  and  a  two-point  switch  S,  is 
located  at  each  end  of  a  block.  No  illuminated  lamp  at 


232  TELEGRAPH   ENGINEERING 

either  end  indicates  that  the  block  is  clear,  and  illuminated 
lamps  at  either  end  denote  that  the  block  is  occupied  by 
a  car  and  that  no  other  car  may  enter  until  these  lights  are 
extinguished.  A  motorman,  reaching  signal  box  A  and 
finding  no  lamps  lit,  moves  switch  Si  to  the  right,  thereby 
causing  lamps  L,  L2,  Z,3,  L\  and  L2'  to  be  illuminated,  and 
proceeds  into  the  block  toward  signal  box  B.  The  lights 
now  displayed  by  both  signal  boxes  permit  no  other  motor- 
man, advancing  from  either  direction,  to  enter  this  occupied 
block.  The  lamp  L,  joined  in  the  signal  wire,  indicates  to 
the  motorman  in  the  block  that  the  signals  are  still  set 
against  advancing  cars.  Upon  reaching  signal  box  J5,  the 
motorman  moves  switch  6*2  to  the  left,  thereby  extinguish- 
ing all  lamps"  and  clearing  the  block.  It  will  be  observed 
that  irrespective  of  the  positions  of  switches  Si  and  S2,  if  no 
lamps  are  lit,  a  movement  of  either  switch  will  light  the 
lamps  at  each  box,  or,  if  lamps  are  illuminated,  a  movement 
of  either  switch  will  extinguish  them.  With  5 50- volt  trolley 
circuits,  five  no- volt  lamps  are  connected  in  series  when 
illuminated. 

With  manually-controlled  block  signal  systems,  arrange- 
ments are  utilized  whereby  each  operator  stationed  along 
the  roadway  cannot  clear  his  own  signal  for  an  approaching 
train  until  it  is  unlocked  through  electrical  means  by  the 
operator  located  at  the  other  end  of  the  block,  his  own 
signal  thereby  displaying  the  danger  signal  to  trains  ad- 
vancing in  the  opposite  direction. 

4.  Location  of  Automatic  Block  Signals.  —  A  home  signal 
is  one  showing  the  condition  of  the  track  directly  in  front 
of  a  train,  and  which,  if  in  the  stop  or  danger  position,  is 
not  to  be  passed  except  as  governed  by  the  rules  of  the 


RAILWAY   SIGNAL  SYSTEMS  233 

railway  company.  A  distant  signal  shows  the  condition 
of  the  track  some  distance  ahead  of  a  train,  and,  if  in  the 
caution  position,  may  be  passed  if  the  train  is  brought  under 
control,  prepared  to  stop  at  the  next  home  signal.  Distant 
signals  should  be  placed  a  distance  in  advance  of  the  home 
signals  permitting  the  fastest  trains  to  be  brought  to  stand- 
still without  overrunning  the  corresponding  home  signals. 
This  braking  distance  may  be  from  1000  to  3000  feet, 
whereas  the  length  of  blocks  is  usually  from  2500  to  8000 
feet;  the  two  distances  depending  upon  traffic,  train  speed 
and  roadway  conditions. 

An  automatic  overlap  system  without  distant  signals  is 
indicated  in  Fig.  5.     Each  home  signal  controls  a  block 

Block  1  Block  2 


Fig.  5. 

plus  an  overlap  equal  to  a  braking  distance  beyond  the  next 
signal  (as  indicated  by  the  dotted  lines),  thereby  insuring 
that  a  stopped  car  is  always  protected  by  a  signal  located 
at  least  a  braking  distance  behind  it.  The  two-position 
semaphores  HI  and  #3  are  shown  held  in  the  clear  position, 
while  Hz  is  in  the  stop  position  owing  to  the  presence  of  the 
car  in  block  2.  The  objection  to  this  overlap  system  is  that 
an  engine  driver  or  a  motorman,  knowing  that  at  times 
there  are  two  signals  at  "  stop  "  between  him  and  the  train 
ahead,  may  be  careless  and  overrun  a  stop  signal  without 
speed  diminution  on  the  belief  that  he  will  have  ample  time 
to  stop,  thereby  courting  danger. 

Because  of  this  objection,  the  automatic  block  systems 


234  TELEGRAPH   ENGINEERING 

represented  in  Figs.  6  and  7  are  preferred  and  generally 
employed  for  double-track  signalling.  In  Fig.  6,  distant 
signals  Dz  and  A  give  advance  indications  of  the  positions 
of  home  signals  Hz  and  HZ  respectively.  When  at  "  cau- 
tion/' a  distant  signal  signifies  to  an  approaching  train: 


Block  1                                                   Block  2 
_J\ A_ 


l fl  I — i — fl  Car     i -*>  i — r—7? 

D™  H^P  oT^  H7!f___ 

Fig.  6. 

expect  to  find  the  next  home  signal  at  "  danger."  For  the 
position  of  the  car  shown  in  the  figure,  signals  HI,  D3  and 
Hz  are  in  the  clear  position,  A  is  in  the  caution  position, 
and  H-i  is  in  the  stop  position. 

In  Fig.  7,  shorter  blocks  are  represented  wherein  a  distant 
signal  is  mounted  on  the  same  mast  with  the  home  signal 

Block  1  Block  2  Block  3 


2-Position 
Two*8.rm  o  \  r  v  o    *  ^^  o    i  M  u  r* 

«g!l8AC. j^V J3v ^4V_ 

3    S!f  1«?L         V JV^ JvL *         V— 

Fig.  7- 

of  the  preceding  block.  The  track  length  controlled  by 
each  home  signal  is  shown  by  the  dotted  lines.  The 
indications  of  the  two-position  two-arm  semaphore  signals 
while  a  car  is  in  block  3  are:  Si  and  54  at  "  clear,"  52  at 
"caution,"  and  £3  at* "  stop."  The  corresponding  indica- 
tions of  three-position  semaphores  are  shown  at  the  bottom 
of  the  figure. 

The    foregoing    double-track    signal    systems    are    not 


RAILWAY   SIGNAL   SYSTEMS  235 

applicable  to  single-track  roads,  because  they  afford  no 
protection  against  oppositely-moving  cars,  but  a  number 
of  automatic  block-signal  systems  have  been  devised  and 
installed  for  single-track  railway  operation.  One  such 
system,  called  the  TDB  (Traffic  Direction  Block)  System, 
has  been  recently  introduced  by  the  Union  Switch  &  Signal 
Company,  and  is  now  in  operation  on  a  number  of  inter- 
urban  electric  railways.  In  this  automatic  block  system, 
the  distance  between  adjacent  sidings  is  a  block  for  oppo- 


•PTr-x 


Fig.  8. 

sitely-moving  cars,  called  an  opposing  block,  and  half  of  this 
distance  is  a  block  for  cars  moving  in  the  same  direction,  or 
a  following  block.  Thus,  each  opposing  block  forms  two 
following  blocks.  :  « 

Fig.  8  shows  the  location  of  semaphore  signals  in  two 
opposing  blocks  of  this  signal  system  and  gives  the  indica- 
tions of  these  signals  as  one  or  more  cars  proceed  through 
the  blocks.  Each  opposing  block  is  equipped  with  four  sig- 


236  TELEGRAPH  ENGINEERING 

nals,  two  being  located  at  its  ends  and  the  other  two  being 
located  a  distance  of  500  to  1000  feet  on  either  side  of  its 
middle  point.  Each  signal  at  a  siding  governs  the  track 
to  the  signal  at  the  next  siding  in  the  case  of  opposing  car 
movements,  but  only  to  the  next  signal  in  the  case  of 
following  car  movements;  whereas  the  intermediate  signals 
govern  the  track  to  the  next  signal  for  following  car  move- 
ments. The  track  sections  controlled  by  each  signal  are 
indicated  at  A  by  broken  lines  for  following  movements  and 
by  dotted  lines  for  opposing  movements.  The  signals  may 
be  of  either  the  light  or  the  semaphore  types,  the  latter, 
with  two-position  indications  in  the  upper  left-hand  quad- 
rant, are  represented  in  the  figure.  This  type  of  semaphore 
is  widely  adopted  on  electric  roads,  because  the  motorman's 
view  of  them  is  not  obstructed  by  the  poles  which  support 
the  trolley  wire. 

An  eastbound  car  R  is  approaching  siding  X  at  B,  Fig.  8, 
and,  consequently,  signal  2  is  in  the  stop  position.  At  C, 
this  car  has  passed  out  of  the  block  to  the  left,  thereby 
clearing  signal  2  and  setting  at  stop  signals  i,  4  and  6. 
A  second  car  S  is  approaching  siding  X  at  D  while  the  first 
car  R  is  approaching  signal  3.  It  is  seen  that  signal  i 
protects  the  rear  of  the  first  car  and  signals  4  and  6  protect 
this  car  against  opposing  car  movements.  At  E,  car  R, 
having  passed  signal  4,  causes  signal  i  to  clear  for  the 
following  car  S.  At  F,  car  S  has  entered  the  first  following 
block  while  car  R  is  in  the  second  following  block;  con- 
sequently, signals  4  and  6  still  protect  the  cars  against 
opposing  car  movements  and  signals  i  and  3  protect  against 
following  car  movements.  The  first  car  has  passed  siding 
Y  at  G  into  the  next  opposing  block,  it  being  observed 
that  both  cars  are  protected  from  both  directions.  The 


RAILWAY  SIGNAL   SYSTEMS 


237 


signal  indications   for  westbound  cars  may  similarly  be 
traced. 

The  four  remaining  diagrams,  H,  I,  J  and  K,  show  the 
signal  indications  for  two  cars  R  and  T  approaching  siding 
Y  from  opposite  directions.  At  /,  the  eastbound  car  has 
taken  the  siding,  and  does  not  affect  any  signals  while  off 
the  main  track. 


Trolley  Wire 


5.  Automatic  Block  Signalling.  —  Automatic  block  sig- 
nal systems  may  be  divided  into  two  groups:  first,  those 
wherein  trains  or  cars  affect  signal  apparatus  on  arrival  at 
definite  places  along  the  roadway  and,  after  passing  these 
points,  leave  the  apparatus  wholly 
beyond  their  control  while  pro- 
ceeding through  the  block,  and 
subsequently,  when  leaving  the 
block,  again  affect  the  apparatus 
to  restore  it  to  its  normal  condi- 
tion; and  second,  those  wherein 
the  train  or  car  is  itself  continu- 
ously in  direct  control  of  the 
signal  for  the  block  over  which  it 
is  passing,  through  the  medium 
of  a  track  circuit.  While  cheaper  to  install,  the  first 
group  does  not  afford  such  thorough  and  continuous 
protection  as  does  the  second  group  of  signal  systems. 
Block  signals  of  the  first  group  were  formerly  used 
on  some  steam  railways,  and  are  now  giving  marked 
satisfaction  on  a  number  of  interurban  electric  railways, 
the  latter  permitting  better  signal  actuation. 

Fig.  9  shows  the  apparatus  at  one  end  of  a  block  for  an 
automatic  signal  system  of  the  first  group  as  applied  to  an 


Fig.  9. 


238  TELEGRAPH  ENGINEERING 

electric  railway.  The  arrangement  is  similar  to  the  manual 
block  signal  described  in  §  3,  except  that  the  switch  S, 
Fig.  4,  is  moved  automatically  when  the  car  passes  the 
block  limits.  This  action  is  accomplished  when  the  trolley 
wheel  reaches  the  signal  contactor  C,  Fig.  9,  for  the  wheel 
then  touches  the  spring  contacts  of  C  and  the  trolley  wire 
simultaneously  and  causes  a  momentary  current  to  flow 
from  the  trolley  wire  through  the  switch-controlling  magnet 
M  to  ground  at  G.  The  consequent  attraction  of  armature 
A  of  this  magnet  permits  the  campiece  c  to  turn  the  ratchet 
wheel  R  through  a  distance  of  one  tooth.  This  causes  the 
notched  wheel  N,  having  half  as  many  crests  as  the  ratchet 
wheel  has  teeth,  to  turn  an  amount  equal  to  the  distance 
from  a  hollow  to  a  crest.  A  projection  of  the  switch  arm 
S  carries  a  small  wheel  W  which  rides  on  the  notched  wheel. 
When  wheel  W  rests  in  a  hollow  (as  shown),  switch  S  closes 
its  left  contact,  and  when  it  rests  on  a  crest,  switch  S  closes 
its  right  contact. 

When  both  signal  sets  of  a  block  are  in  the  position 
illustrated,  no  current  traverses  the  signal  wire  with  its 
lamps  L,  thereby  giving  the  indication  that  the  block  is 
clear.  When  a  car  enters  the  block,  the  magnet  is  momen- 
tarily energized  and  the  attraction  of  its  armature  causes 
a  limited  rotary  movement  of  wheels  R  and  N.  Switch  5, 
in  consequence,  moves. to  its  opposite  position  and  closes 
the  right  and  opens  the  left  contact.  This  action  illumi- 
nates lamp  L  and  the  other  lamps  connected  in  the  signal 
wire,  thereby  giving  the  stop  indication  to  other  cars  ad- 
vancing in  the  same  or  in  the  opposite  direction.  As  the 
car  moves  out  of  the  block,  the  switch  at  the  other  signal  is 
similarly  moved  and  the  lamps  are  extinguished,  thus  again 
clearing  the  block. 


RAILWAY   SIGNAL   SYSTEMS  239 

The  Chapman  Automatic  Signal  System  employs  con- 
tactors which  are  returned  by  a  spring  to  their  normal 
position  after  they  have  been  moved  in  either  direction 
by  a  trolley  wheel.  The  signals  used  with  this  system  are 
of  the  semaphore  type  and  are  actuated  by  electromagnets. 
There  are  three  magnets  in  each  signal,  two  for  controlling 
the  indication  of  the  semaphore  arm,  and  the  third  for 
closing  certain  contacts  upon  momentary  actuation  as  a 
car  enters  a  block  section.  The  three  positions  of  the 
semaphore  blade  indicate :  horizontal  —  car  approaching  in 
opposite  direction,  inclined  downward  45  degrees  —  clear, 
vertically  downward  —  car  in  block  receding  from  you. 

Insulating 
Track  Joints 

j  Track  Rails  t 

* 


Fig.  10. 

The  principle  of  all  automatic  block  signal  systems  of  the 
second  group  is  the  operation  of  a  relay  whenever  a  pair  of 
wheels  with  their  connecting  axle  enters  or  leaves  a  block. 
The  scheme  of  such  systems  for  steam  railroads  is  illustrated 
in  Fig.  10.  A  battery  is  located  at  one  end  of  a  block  and 
connected  across  the  two  track  rails  of  a  section,  which  are 
separated  from  the  rails  of  the  adjacent  sections  by  insulat- 
ing joints.  The  rails  serve  as  conductors  for  the  current 
from  battery  b  to  a  track  relay  R,  which  is  located  at  the 
other  end  of  the  block  and  likewise  connected  across  the 
track  rails.  The  relay  controls  through  its  contact  points 
the  local  circuit  of  battery  B  and  the  semaphore  signal  S. 
When  no  car  is  in  the  block,  relay  R  is  energized  and  the 


240 


TELEGRAPH   ENGINEERING 


local  circuit  is  closed,  thereby  holding  the  signal  at  clear. 
When  a  car  enters  the  block,  the  battery  b  is  short-circuited 
by  the  car  wheels  and  axles,  and  the  relay  is  deprived  of 
current.  The  consequent  opening  of  the  local  circuit  at 
the  relay  sets  the  signal  in  the  danger  position.  The 
battery  and  relay  are  placed  at  opposite  ends  of  a  track 
section,  because  this  arrangement  protects  against  broken 
rails  and  also  indicates  open  bonds  between  rail-lengths. 
Either  primary  or  storage  batteries  are  used,  and  these 
are  located  in  battery  wells  or  chutes  beside  the  tracks. 
When  distant  signals  are  used  with  the  scheme  repre- 
sented in  Fig.  10,  polar-neutral  track  relays  are  employed, 


Block  2 


Block  1 


Fig.  ii. 

their  neutral  armatures  controlling  the  home  signals  and 
their  polarized  armatures  controlling  the  distant  signals; 
the  operation  of  a  home  semaphore  blade  moving  a  pole- 
changer  for  reversing  the  current  in  the  relay  of  the  pre- 
ceding block.  This  system  is  called  the  polarized  or 
"  wireless "  automatic  block  signal  system. 

Each  signal  may  be  controlled  by  any  number  of  track- 
circuit  relays,  and  each  relay  may  have  a  plurality  of 
contacts.  Thus,  Fig.  n  shows  the  scheme  of  connections 
for  normally-clear  two-arm  semaphores  (located  as  in 
Fig.  7)  for  two  blocks  of  a  track  intended  for  traffic  in  one 
direction  only.  Each  block  is  shown  divided  into  two  track 


RAILWAY   SIGNAL   SYSTEMS 


241 


sections  a  and  b,  so  as  to  increase  the  reliability  of  the  track 
circuits  by  reducing  the  effect  of  current  leakage  from  one 
rail  to  the  other  along  ballast  and  ties.  Track  relays  RI 
and  R2  control  the  home  blade  HI  of  block  i,  relays  R3  and 
RI  control  the  home  blade  H2  of  block  2,  and  relays  RI,  R2, 
R3  and  R±  control  the  distant  blade  D2.  The  operation 
of  the  signals  for  indicating  the  track  conditions  with  the 
passage  of  a  train  can  be  understood  readily  from  an 


Fig.  12. 

examination  of  the  diagram,  if  it  be  remembered  that  each 
semaphore  blade  assumes  the  horizontal  position  whenever 
its  local  circuit  is  opened  at  a  relay  contact.  For  the 
position  of  the  train  indicated,  the  contacts  of  relay  RI  are 
open  and,  therefore,  home  blade  HI  and  distant  blades  A 
and  DZ  will  be  horizontal. 

A  large  variety  of  track  circuits  is  utilized  in  practice 
for  different  types  of   automatic   block   signalling,  using 


242 


TELEGRAPH   ENGINEERING 


normally-clear  or  normally-danger  signals  on  single-  or 
double-track  steam  and  electric  roads  in  connection  with 
overlap,  non-overlap  or  preliminary-section  systems. 

The  appearances  of  two  .types  of  direct-current  track 
relays  manufactured  by  the  General  Railway  Signal  Com- 
pany are  shown  in  Figs.  12  and  13.  That  shown  in  Fig.  12 
is  the  Taylor  tractive-type  relay  and  has  4  contacting  fin- 


r 


Fig.  13- 

gers,  each  with  front  and  back  contacts ;  that  shown  in  Fig. 
13  is  a  three-position  mo  tor- type  relay  also  with  4  contact- 
ing fingers,  the  closing  of  one  or  the  other  sets  of  contacts 
being  accomplished  by  a  partial  rotation  of  the  motor 
armature  through  the  medium  of  an  eccentric  link. 


6.   Automatic   Block   Signals   on   Electric   Railways.  — 
Signalling  on  electric  railways  is  accomplished  in  a  some- 


RAILWAY   SIGNAL  SYSTEMS  243 

what  different  manner  from  that  employed  on  steam  rail- 
roads as  just  described,  because  the  track  rails  are  utilized 
as  a  return  path  for  the  current  required  in  car  propulsion. 
One-rail  Block  Signal  System.  —  Where  it  is  possible  to 
spare  the  conductivity  of  one  track  rail  in  the  return  of  the 
propulsion  current,  as  on  elevated  roads  where  the  support- 
ing structure  serves  also  as  a  return  path,  one  track  rail  is 
sectionalized  and  used  for  block  signalling.  Alternating 
current  is  now  usually  employed  for  signalling  with  this 
arrangement,  requiring  the  use,  on  direct-current  railways, 
of  relays  that  are  responsive  to  alternating  current  but  not 
to  direct  current,  and,  on  alternating-current  railways,  of 
relays  that  are  responsive  only  to  alternating  current  of 
higher  frequency  than  the  propulsion  current. 

Return  Rail  for  Propulsion  Current 


A.  C.  Signal  Mains 
Fig.  14. 

Fig.  14  shows  the  scheme  of  connections  of  the  one-rail 
automatic  block  signalling  system.  The  transformers  T 
supply  alternating  current  to  the  "  exit  end  "  of  each  track 
section  from  the  alternating-current  supply  mains.  The 
alternating-current  relays  Rj  connected  at  the  opposite  end 
of  the  track  sections,  control  the  operation  of  signals  5 
through  the  local  batteries  B,  as  before,  or  through  alter- 
nating-current motors  fed  by  transformers  joined  to  the 
signal  mains.  Each  relay  is  shunted  by  an  impedance  to 
keep  direct  currents  from  the  instrument.  Usual  trans- 
mission voltages  are  from  2200  to  4400,  and  at  each  block 


244 


TELEGRAPH  ENGINEERING 


are  stepped  down  to  220  or  no  volts  for  the  operation  of 
alternating-current  semaphore  motors,  and  to  6  to  15  volts 
for  the  operation  of  the  track  circuits  and  lamp  signals. 

This  system  is  used  in  the  New  York  Subway,  where 
approximately  700  signals,  500  track  circuits  and  40  inter- 
locking plants  are  used.  During  the  morning  and  evening 
rush  hours  150  subway  trains  per  hour  pass  g6th  Street, 
this  heavy  traffic  demanding  blocks  as  short  as  1500  feet. 
The  signal  mains  supply  6o-cycle  current  at  500  volts  to  the 
block  transformers,  each  having  two  secondary  windings, 
one  which  feeds  the  track  circuit  at  10  volts,  and  the  other 
which  feeds  the  lamp  signal  circuits  at  50  volts.  The  valve- 
Track  Rail 


A. C. Signal  Mains 
Fig.  15. 

controlling  magnets  of  the  electro-pneumatic  signal  mecha- 
nisms are  operated  by  direct  current  at  16  volts  supplied 
by  storage  batteries. 

Two-rail  Block  Signal  System.  —  Both  track  rails  of  an 
electric  railway  may  be  used  simultaneously  as  a  return  for 
the  propulsion  current  and  as  conductors  for  the  signalling 
current  by  the  employment  of  impedance  bonds  placed 
between  and  connected  across  the  track  rails  at  both  ends 
of  each  track  section.  These  bonds  are  shown  at  I  in 
Fig.  15,  the  middle  points  of  the  windings  of  adjacent  bonds 
being  connected  together.  In  other  respects,  the  one-rail 


RAILWAY   SIGNAL  SYSTEMS 


245 


and  two-rail  signal  systems  are  identical;    compare  the 
schemes  of  Figs.  14  and  15. 

The  impedance  bonds  have  little  resistance  but  large 
inductance,  for  they  consist  of  heavy  windings  of  copper 
around  massive  laminated-iron  cores  as  illustrated  in  Fig. 
1 6.  For  600- volt  railways  the  resistance  of  a  bond  may 


PLAN  VIEW-COVER  REMOVED. 


SECTIONAL  SIDE  VIEW 

Fig.  1 6. 

be  from  0.0004  to  0.0015  ohm.  The  propulsion  current,  in 
being  carried  around  the  insulating  joints  which  separate 
the  track  signal  circuits  from  each  other,  flows  differentially 
through  the  bonds  and,  consequently,  does  not  magnetize 
their  cores.  Therefore,  the  propulsion  current  will  not 
affect  the  signalling  apparatus.  The  impedance  of  the 
bonds  to  the  alternating  current  used  for  signalling  is  so 


246  TELEGRAPH  ENGINEERING 

great  in  comparison  with  that  of  the  relays  that  the 
presence  of  the  bonds  will  not  affect  the  operation  of  the 
alternating-current  track  relays. 

The  two-rail  block  signal  system  is  installed  on  a  number 
of  direct-current  railways,  a  few  of  which  are:  the  West 
Jersey  and  Seashore  Railroad,  the  Washington,  Baltimore 
&  Annapolis  Electric  Railroad,  the  Hudson  and  Manhattan 
Railroad,  and  in  the  electrified  zones  of  the  New  York 
Central,  the  Pennsylvania,  and  the  Southern  Pacific 
Railroads. 

This  block  signal  system  is  also  used  on  alternating- 
current  electric  railways,  the  relays  being  designed  not  to 
respond  to  the  propulsion  currents,  but  to  respond  to  cur- 
rents of  a  higher  frequency  used  in  signalling.  Thus,  on 
25-cycle  electric  railways  the  signalling  is  usually  accom- 
plished by  currents  of  6o-cycle  frequency.  Signal  installa- 
tions of  this  type  include  the  New  York,  Westchester  and 
Boston  Railway,  the  Chicago,  Lake  Shore  &  South  Bend 
Railway,  and  the  electrified  zone  of  the  New  York,  New 
Haven  and  Hartford  Railroad. 

Alternating-current  Track  Relays.  —  The  vane- type  al- 
ternating-current relay,  shown  in  Fig.  17,  made  by  the 
Union  Switch  &  Signal  Company  is  widely  used  with  one- 
rail  block  signal  systems.  It  consists  of  a  C-shaped 
laminated  core  carrying  two  field  coils,  one  on  either  side  of 
the  core  air-gap.  The  pole-pieces  of  the  core  are  provided 
with  single  turns  of  wire  short-circuited  upon  themselves, 
called  shading  coils.  An  aluminum  vane,  pivoted  in  jewel 
bearings,  is  arranged  to  move  up  and  down  in  the  air-gap. 
When  an  alternating  current  traverses  the  field  coils,  a 
shifting  magnetic  flux  is  established  at  the  air-gap  with  the 
aid  of  the  shading  coils,  which  flux  causes  an  upward 


RAILWAY   SIGNAL  SYSTEMS 


247 


movement  of  the  vane.  Contact  fingers  mounted  on  the 
shaft  carrying  the  vane  are  thereby  brought  against  sta- 
tionary contacts  connecting  with  the  terminals  on  the  cover. 


Fig.  17. 

Fig.  1 8  shows  the  appearance  of  the  centrifugal  frequency 
track  relay  made  by  the  same  concern  and  used  on  alter- 
nating-current electric  railways  employing  the  two-rail 
block  signal  system.  Other  types  of  alternating-current  re- 
lays for  both  one-rail  and  two-rail  automatic  signal  systems 
are  available. 

7.  Interlocking  Plant  Signals.  —  Track  switches  and 
signals  at  railroad  crossings,  junctions,  crossovers,  draw- 
bridges and  terminal  yards  are  operated  mechanically, 
electrically  or  electro-pneumatically  and  are  actuated  by 
the  levers  of  interlocking  machines  under  the  control  of 
levermen.  An  interlocking  machine  is  usually  placed  as 
close  as  possible  to  the  devices  which  it  controls,  but 
numerous  such  machines  are  in  use  which  are  6000  feet 


248 


TELEGRAPH  ENGINEERING 


distant  from  some  of  the  devices  controlled.  The  use  of 
mechanical  interlocking  machines  is  restricted  to  short 
distances,  say  up  to  1000  feet;  but  the  electric  and  electro- 
pneumatic  machines  may  be  used  for  controlling  devices 
at  great  distances.  Fig.  19  shows  the  Unit  Lever  type 
Electric  Interlocking  Machine,  in  combination  with  the 


Fig.  18. 

operating  switchboard  and  indicator  groups,  made  by  the 
General  Railway  Signal  Company.  This  machine  has 
38  levers  for  operating  switches  and  signals  and  has  14 
indicators.  Such  indicators  are  used  for  checking  the 
correspondence  of  movement  between  the  lever  and  the 
device  which  it  operates,  the  indications  being  received 
after  the  operation  of  the  device  has  been  properly  com- 
pleted. The  movement  of  a  lever  locks  all  levers  conflicting 
with  its  new  position  and  operates  the  device  which  it 


RAILWAY   SIGNAL  SYSTEMS 


249 


controls.  This  interlocking  of  levers  is  performed  at  the 
"  locking  bed  "  located  at  the  front  of  the  machine,  by 
horizontal  locking  bars  carrying  V-shaped  dogs  which  en- 
gage notches  in  vertical  tappet  bars.  Upon  moving  a  lever, 
its  tappet  bar  is  moved  vertically  and  one  or  more  locking 
bars  are  moved  by  the  dogs  which  engage  them,  and  the 


Fig.  19. 

dogs  carried  by  these  bars  move  into  the  notches  on  cer- 
tain tappet  bars,  thus  locking  their  corresponding  levers. 

A  simple  illustration  of  the  function  of  an  interlocking 
machine  will  be  considered  in  connection  with  Fig.  20 
which  represents  the  position  of  signals  and  derails  at  a 
single-track  railway  crossing.  In  this  diagram  i,  6,  7  and 
12  are  distant  signals,  2,  5,  8  and  n  are  home  signals,  and 
3,  4,  9  and  10  are  derails,  all  devices  being  represented  in 
their  normal  positions,  that  is,  the  derails  open  and  sema- 
phore blades  horizontal.  To  permit  a  train  to  pass  from 


25° 


TELEGRAPH  ENGINEERING 


A  to  B  requires  that  derails  3  and  4,  and  signals  i  and  2 
must  be  reversed,  and  for  proper  protection  to  this  train 
while  on  the  crossing,  derails  9  and  10,  and  signals  5,  6,  7, 
8,  ii  and  12  must  be  held  normal.  This  is  accomplished 
by  the  levers  of  the  interlocking  machine,  which  bear  the 
same  numbers  as  their  corresponding  devices.  Therefore, 


^  an. 


10 


B 
Fig.  20. 


derail  levers  3  and  4  when  reversed  should  each  lock  derail 
levers  9  and  10  normal,  and  conversely.  Further,  to  pre- 
vent levers  8  and  n  being  reversed  before  levers  9  and  10 
are  reversed,  it  is  necessary  that  levers  8  and  n  when 
reversed  should  each  lock  levers  9  and  10  reversed.  Each 
distant  signal  when  reversed  locks  its  home  signal  reversed. 
Finally,  lever  2  when  reversed  should  lock  lever  5  normal, 
and  lever  8  when  reversed  should  lock  n  normal.  These 
operations  may  be  tabulated  in  the  form  of  a  chart  as  shown 
on  the  next  page,  thus  forming  the  locking  sheet  for  the 


RAILWAY   SIGNAL  SYSTEMS 


251 


interlocking  machine.  It  will  be  observed  that  converse 
lockings  are  not  duplicated,  for  it  is  understood  that  if  one 
lever  locks  another  lever  normal,  the  opposite  is  also  true, 
that  is,  the  latter  lever  locks  the  former  normal. 


Lever 

When  reversed  locks 

Reversed 

Normal 

I 

2 

2 

3       4 

5 

3 

9     10 

4 

9     10 

5 

3       4 

6 

5 

7 

8 

8 

9     10 

9 

10 

ii 

9     10 

8 

12 

ii 

PROBLEMS 

1.  At  what  minimum  separation  may  two  cars  travelling  m  the 
same  direction  be  operated  at  full  speed  over  a  track  with  the  signal 
arrangements  shown  in  Figs.  5,  6,  7  and  8?    Express  the  result  in  each 
case  in  terms  of  block  lengths. 

2.  Describe  the  operation  of  the  relays  and  semaphore  signals  of 
the  automatic  block  signal  system  illustrated  in  Fig.  n  as  a  train 
advances  from  one  track  section  to  another. 

3.  A  1.3  volt  primary  battery  supplies  0.5  ampere  to  one  end  of 
a  track  circuit  3600  feet  long,  at  the  other  end  of  which  is  a  3.5  ohm 
track  relay.    The  voltage  measured  from  rail  to  rail  at  frequent 
intervals  along  this  track  section  showed  a  drop  of  3.5  millivolts  for 
each  3o-ft.  track  length,  this  being  due  to  resistance  of  track  and 
bonds,  and  to  leakage  across  ballast  and  ties.     What  percentage  of 
the  battery  current  traverses  the  relay? 


252  TELEGRAPH  ENGINEERING 

4.  Draw  up  the  locking  sheet  for  an  interlocking  machine  to  be 
installed  at  a  single-track  railway  junction  at  which  the  signals  and 
switches  are  located  as  shown  below.  The  distant  signals  i,  2,  8  and 
ii  show  the  indications  of  the  home  signals  3, 4,  7  and  10  respectively; 


12  34 

signals  i  and  3  apply  to  route  AC,  and  signals  2  and  4  apply  to  route 
AB.  Switch  5  is  shown  normally  open,  and  the  derails  6  and  9  are 
normally  set  to  derail.  It  should  be  noted  that  lever  5  of  the  machine 
is  under  the  immediate  control  of  either  lever  6  or  9,  for  lever  3  (or  4) 
cannot  be  reversed  until  lever  9  (or  6)  has  been  reversed. 


CHAPTER   IX 

TELEGRAPH  LINES  AND   CABLES 

I.  Aerial  Open  Lines. —  Line  conductors  for  telegraphic 
signalling  may  be:  bare  wires  mounted  overhead  at  some 
distance  from  each  other  on  poles  or  towers;  insulated 
wires  grouped  together,  forming  a  cable,  and  usually  en- 
closed in  a  lead  sheath,  either  suspended  at  short  intervals 
from  a  steel  cable  fastened  to  poles  or  else  drawn  into 
underground  conduits;  or  cables  comprising  one  or  more 
well-insulated  conductors  surrounded  by  a  waterproof 
covering  and  steel  armor,  as  in  submarine  cables.  These 
types  will  be  considered  in  the  order  mentioned. 

For  overhead  telegraph  lines  galvanized  iron  of  various 
grades,  hard-drawn  copper  and  sometimes  steel  or  copper- 
clad  steel  wire  are  employed.  The  sizes,  weights  and  re- 
sistances of  the  conductors  generally  used  are  given  in  §  8 
of  Chap.  I.  The  increasing  adoption  of  copper  for  tele- 
graph lines  is  due  to  its  low  resistance  (about  one-sixth 
that  of  iron),  its  high  tensile  strength  (45,000  to  68,000 
pounds  per  square  inch)  and  its  non-corrosion  under  ordi- 
nary atmospheric  conditions. 

Joints.  —  Lengths  of  iron  line  wire  are  usually  joined  by 
placing  the  two  ends  side  by  side  and  winding  half  the 
overlap  of  each  wire  spirally  around  the  other;  this  is 
called  the  Western  Union  joint.  For  joining  copper  line 
wires  the  Mclntyre  connector  is  widely  used,  which  con- 
sists of  a  double  copper  tube,  of  correct  size  to  fit  the  line 

253 


254  TELEGRAPH  ENGINEERING 

wire.  The  ends  of  the  wires  are  inserted  from  opposite 
ends,  one  through  each  of  the  twin  tubes,  and  the  sleeve 
is  then  twisted  through  three  complete  turns.  Such  joints 
do  not  require  soldering. 

Insulators. — The  insulators  f6r  supporting  bare  overhead 
telegraph  lines  in  this  country  are  generally  constructed  of 
glass,  and  sometimes  of  porcelain.  The  design  of  the  stand- 
ard form  of  insulator  is  shown  at  the  left  of  Fig.  i,  the 
dimensions  in  inches  being  indicated  thereon.  Its  small 
diameter,  coupled  with  the  relatively  large  distance  along 
the  surface  from  the  wire  groove  to  the  insulator  pin,  con- 
duces to  the  maintenance  of  high-insulation  resistance 
despite  accumulations  of  dirt  and  other  foreign  matter  on 
the  insulator  surface.  The  insulator  at  the  right  of  Fig.  i 
shows  the  standard  form  of  two-piece  transposition  insu- 
lator. Insulators  having  double  flanges  or  "  petticoats  "  at 
the  bottom  are  sometimes  used  when  greater  insulation 
resistance  is  desired. 

The  line  wire  when  attached  to  the  insulators  is  not 
passed  around  the  insulator  but  is  laid  in  the  groove  at 
one  side  and  is  tied  in  this  position  by  short  pieces  of 
wire  of  the  same  size  as  the  line  wire  and  which  pass  around 
the  insulator.  The  middle  portion  of  Fig.  i  shows  the 
standard  type  of  insulator  pin  for  supporting  the  insu- 
lators on  the  pole  cross-arms.  They  are  commonly  made 
of  chestnut,  locust  or  oak,  both  the  shank  and  thread  being 
tapered.  Wood-top  steel  pins  and  wood  bracket-pins  are 
also  used,  the  latter  being  fastened  directly  to  the  pole 

(Fig.  4). 

Poles.  —  Wooden  poles  are  most  generally  used  for  sup- 
porting aerial  telegraph  or  telephone  lines,  except  where 
unusually  large  spans  demand  strong  towers  of  steel  or  re- 


TELEGRAPH  LINES  AND   CABLES 


255 


inforced  concrete.  In  this  country  white  cedar,  chestnut, 
cypress,  pine  and  redwood  poles  are  principally  used  for 
this  purpose.  These  poles  are  from  20  to  80  feet  in  height, 
but  those  from  25  to  40  feet  are  the  more  usual.  The 
height  of  poles  to  be  used  in  a  given  locality  is  governed 
by  several  conditions,  such  as  ordinances  requiring  a 
minimum  distance  of  the  lowest  wire  above  the  ground, 


non-interference  of  the  wires  with  the  possible  activities  of 
the  fire  department,  clearance  at  trolley  and  railway  cross- 
ings, etc.  The  poles  are  from  5  to  8  inches  in  diameter  at 
the  top,  with  an  increase  in  diameter  of  about  one  inch  in 
every  10  feet  toward  the  bottom.  Poles  are  set  from  5 
to  10  feet  into  the  ground,  according  to  the  height  of  the 
pole  and  the  nature  of  the  soil.  In  many  cases  it  is  de- 
sirable to  treat  the  lower  ends  of  the  poles  so  as  to  mini- 
mize decay  where  they  are  embedded  in  the  ground.  This 


256  TELEGRAPH   ENGINEERING 

treatment  consists  of  applying  a  preserving  fluid,  such  as 
creosote  or  carbolineum  oil,  applied  by  pressure,  dipping  or 
by  brush.  Poles  decayed  at  the  ground  may  be  repaired 
by  placing  a  rigid  collarvof  reinforced  concrete  around  the 
decayed  portion  of  the  poles. 

The  size  of  the  poles  should  be  selected  so  that  the 
transverse  forces,  due  to  the  tension  in  the  wires  at  turns 
in  the  line  and  to  wind  pressure  on  poles  and  wires,  do  not 
exceed  the  breaking  stress  of  the  pole.  The  pull,  exerted 
at  the  center  of  load  at  a  point  Lc  feet  above  the  ground, 
that  will  break  a  circular-sectioned  pole  having  a  diameter 
d  feet  at  the  ground  line,  may  be  expressed  as 

F  =      -S  pounds,  (i) 


where  A  is  the  cross-sectional  area  of  the  pole  at  the  ground 
in  square  inches  and  S  is  the  tensile  strength  in  pounds 
per  square  inch.  Accepted  values  of  the  maximum  fibre 
stress  S  for  some  woods  are  given  below: 


Chestnut 6,000-10,000 

Cypress 5,ooo-  8,000 

White  cedar 4,000-  8,000 

Yellow  pine 4,000-  8,000 


pounds  per  sq.  in. 


In  proper  designs  much  lower  values  of  this  maximum 
fibre  stress  are  employed,  thereby  allowing  a  considerable 
factor  of  safety. 

At  a  turn  in  the  line,  if  the  horizontal  angle  between  the 
directions  of  the  wires  at  either  side  of  the  pole  be  6,  and 
the  tension  in  each  of  N  wires  be  T  pounds,  then  the  trans- 
verse force  acting  on  the  pole  at  a  height  Lc  feet  above  the 
ground  is 

F  =  2  NT  cos  -  pounds,  (2) 


TELEGRAPH  LINES   AND   CABLES  257 

which  assumes  that  the  tension  in  the  wires  is  the  same  on 
both  sides  of  the  pole.  The  wind  pressure  on  the  pole, 
having  an  average  diameter  of  da  feet  and  a  height  of  H 
feet  above  the  ground,  will  be  equivalent  to  a  force  of 
KdaH  pounds  acting  at  the  center  of  the  pole,  where  K  is 
the  wind  pressure  per  square  foot  of  projected  pole  area, 
usually  taken  as  a  maximum  of  8  pounds.  This  force  act- 
ing at  the  center  of  the  pole  may  be  replaced  by  a  force 
at  the  center  of  load  of,  say,  0.6  KdaH  pounds  acting  at  a 
point  distant  Lc  or  f  of  the  pole  height  from  the  bottom. 
If  the  wind  blows  in  the  direction  of  the  resultant  trans- 
verse force  F',  the  wind  pressure  on  the  wires  will  be 

— !sin-,  where  /  is  the  distance  between  poles  in  feet, 
12          2 

and  di  is  the  diameter  of  each  conductor  over  a  possible 
ice  coating,  in  inches.  Therefore  the  maximum  wind 
pressure  on  the  pole  and  wires  which  may  assist  the  trans- 
verse force  on  the  pole  at  a  turn  in  the  line  is 

F"  =  K  (0.6  dJI  +  0.0833  Nidi  sin  -}  pounds,       (3) 

and  consequently  a  pole  should  be  selected  so  that 
F>F'  +  F" 

with  a  considerable  factor  of  safety.  If  this  requirement 
demands  a  pole  of  unusually  large  diameter  for  an  assumed 
factor  of  safety  and  for  a  given  angular  change  in  the  direc- 
tion of  the  pole  line,  a  smaller  pole  may  be  used  if  rein- 
forced by  the  use  of  guy  wires  or  braces  of  suitable  types. 
Such  reinforcement  is  generally  utilized  with  terminal 
poles,  with  poles  at  the  ends  of  long  wire  spans  or  with 
poles  near  a  curve  or  corner.  Fig.  2  indicates  the  method 
of  guying  a  line  at  a  road  crossing. 


TELEGRAPH  ENGINEERING 


To  consider  a  specific  example,  assume  a  bend  of  160 
degrees  in  a  24-wire,  3-arm  pole  line  of  No.  9  B.  &  S.  gage 
copper  wire,  supported  on  white-cedar  poles  projecting  30 
feet  above  the  ground  and  spaced  130  feet  apart.  If  the 
maximum  fibre  stress  be  taken  as  6000  pounds  per  square 
inch,  and  the  diameter  of  the  pole  at  the  ground  is  i  foot, 
and  at  the  top  is  8  inches,  the  transverse  force  on  the 


Fig.  2. 

corner  pole  acting  at  the  center  of  load  (say  at  a  point  25 
feet  from  the  ground)  necessary  to  break  the  pole  is 

„      IT  (6)2  X  i, 

F  =    a  s/    r    6oo°  =  3390  pounds. 

o  A  25 

If  the  tension  of  each  wire  be  200  pounds,  the  transverse 
force  due  to  wire  tension  at  the  corner  pole  is 

Ff  =  2  X  24  X  200 cos—   -  =  1670  pounds, 

and  if  the  outside  diameter  of  the  ice-covered  wire  be 
taken  as  1.114  inches,  thereby  allowing  \  inch  of  ice  all 


TELEGRAPH  LINES   AND   CABLES  259 

around  the  conductors,  the  transverse  force  due  to  wind 
pressure  is 

F"  =  8(0.6^—30  +  0.0833  X  24X130X1.114  sin—) 

\2Xl2  2     / 

=  2376  pounds. 

Thus,  the  total  transverse  force  that  may  act  on  the  pole 
under  consideration  is  1670  +  2376  =  4046  pounds,  a 
force  greater  than  the  assumed  breaking  stress  of  the  pole, 
or  3390  pounds.  Therefore  this  corner  pole  must  be 
firmly  guyed  or  braced  in  order  to  maintain  telegraphic 
service  over  this  line  in  times  of  severe  wind  and  sleet. 

Cross-arms.  —  The  cross-arms  for  a  telegraph  pole  are 
made  of  sound,  thoroughly  seasoned  straight-grained  tim- 
ber, either  creosoted  or  painted.  The  standard  cross-arms 
measure  3^  by  4^  inches,  and  may  vary  in  length  from  3 
to  10  feet,  depending  upon  the  number  of  wires  accom- 
modated. These  cross-arms  are  attached  to  the  poles  by 
placing  them  in  gains  or  slots  cut  in  the  poles  and  securing 
them  in  position  either  by  lag-screws  or  by  bolts  which 
pass  through  the  pole. 

The  strength  of  standard  cross-arms  is  indicated  in 
the  following  table,  which  gives  the  results  of  recent 
tests  conducted  by  the  Forest  Service  on  6-foot,  6-pin 
cross-arms : 

Average  maximum  downward 
load  in  pounds 

Longleaf  pine  (75  per  cent  heart) 10,180 

Longleaf  pine  (100  per  cent  heart) 9,?8o 

Longleaf  pine  (50  per  cent  heart) 8,980 

Shortleaf  pine 9,260 

Shortleaf  pine  (creosoted) 7,650 

Douglas  fir 7,590 

White  cedar 5,200 


260 


TELEGRAPH   ENGINEERING 


Cross-arms  are  further  secured  by  iron  or  steel  braces,  as 
indicated  in  Fig.  3,  which  also  shows  the  usual  spacing  in 
inches  of  insulators  and  cross-arms. 

Poles  at  line  terminals  or  at  the  ends  of  long  spans  are 


g  a  a  a 


9  9  a 


Fig.  3. 

usually  provided  with  double  cross-arms,  placed  on  op- 
posite sides  of  the  poles  and  bolted  together. 

Lightning  Arresters.  —  To  protect  pole  lines  against  de- 
struction by  lightning,  it  is  common  practice  to  lead  a 
ground  wire  to  the  top  of  at  least  every  tenth  pole.  Fig.  4 
shows  one  arrangement  employing  a  double-grooved  in- 


TELEGRAPH  LINES  AND   CABLES 


261 


sulator  mounted  on  a  bracket  pin.    It  will  be  observed 
that  a  small  gap  is  formed  between  the  ground  wire  and 
the  line  wire,  over  which  a  lightning  discharge  may  take 
place    and    pass    to    ground.     The 
lower  end  of  the  ground  wire  usually 
connects  with  an  iron  pipe  driven 
into  the  ground  at  least  two  feet 
away  from  the  pole. 


WIRE 


2.  Wire  Spans.  —  In  suspending 
wires  from  pole  cross-arms,  the  ten- 
sion of  the  wire  should  be  such  that 
at  the  lowest  attainable  temperature 
the  tension  due  to  the  weight  of 
the  wire  with  possible  coverings  of  sleet  and  snow  and 
due  to  wind  pressure  must  not  exceed  a  predetermined 
value.  The  physical  constants  of  various  sizes  of  hard- 


Fig.  4- 


Fig.  5. 

drawn  copper  and  galvanized  iron  wire  are  given  in  the 
following  table.  The  values  of  tensile  strength  given 
in  this  table  should  not  be  used  directly  in  determining 
the  proportions  of  wire  spans,  but  should  be  divided  by  a 
proper  factor  of  safety,  say  2  to  4,  so  that  the  wire  may 


262 


TELEGRAPH   ENGINEERING 


withstand  excessive  momentary  loads  to  which  the  line 
may  be  occasionally  subjected. 


Hard-drawn  Copper 

Modulus  of  Elasticity  =  16,000,000  pounds 
per  sq.  in. 

Coefficient  of  Expansion  =  0.0000095  per  deg 
fahr. 


Galvanized  Iron  Wire 

Modulus  of  Elasticity  =  26,000,000  pounds 

per  sq.  in. 

Coefficient  of  Expansion  =  0.0000067  per  deg. 
fahr. 


B.&S. 
Gage 
No 

Diam- 
eter in 
inches 

Area 
in 
square 
inches 

Tensile 
strength 
in 
pounds 

Weight 
in 
pounds 
per 
foot 

S.W.G. 
No. 

Diam- 
eter in 
inches 

Area 
in 
square 
inches 

Tensile 
strength 
in 
pounds 

Weight 
in 
pounds 
per 
foot 

9 

O.II4 

0.01028 

630 

o  .  0396 

4 

0.238 

0.0445 

2I2O 

0.1490 

10 

0.102 

0.00815 

525 

0.0314 

5 

O.22O 

0.0380 

1820 

0.1275 

ii 

O.OQI 

0  .  00646 

420 

0.0249 

6 

0.203 

0.0324 

*55° 

0.1085 

12 

O.oSl 

0.00513 

330 

0.0198 

7 

0.180 

0.0254 

I2IO 

0.0853 

13 

0.072 

0  .  00407 

270 

0.0157 

8 

0.165 

0.0214 

IO2O 

0.0716 

14 

0.064 

0.00323 

213 

O.OI24 

9 

0.148 

0.0172 

820 

0.0578 

10 

0-134 

0.0141 

670 

0.0474 

In  determining  the  proper  sag  of  a  wire  span,  the  maxi- 
mum weight  of  the  wire  with  sleet  or  ice  loads  must  be 
known.  In  view  of  the  variation  of  climatic  conditions,  it 
is  usual  to  assume  an  ice  coating  of  f  inch  thickness  all 
around  the  wire  as  the  severest  load,  the  weight  being 
0.033  pound  per  cubic  inch.  Wind  pressure  must  also  be 
considered,  this  force  being  assumed  horizontal  and  per- 
pendicular to  the  wire.  The  maximum  wind  pressure  may 
be  taken  as  8  pounds  per  square  foot  of  projected  area  of 
the  wire  or  of  the  ice  cylinder;  this  value  corresponds  ap- 
proximately to  a  wind  velocity  of  60  miles  per  hour.  The 
minimum  temperature  may  be  considered  as  —  20  deg.  fahr. 
and  the  maximum  temperature  as  120  deg.  fahr.,  these 
temperatures  being  reasonable  values  for  the  northern 
part  of  this  country. 

Let  wi  =  weight  of  wire  and  ice  per  foot  of  wire  length, 


TELEGRAPH   LINES  AND   CABLES  263 

and  w<t  =  wind  pressure  per  foot  of  wire  length,  then  the 
resultant  force  per  foot  will  be 


W  =    Vwi2  +  Wi2,  (4) 

and  the  wire  will  assume  the  position  indicated  in  Fig.  5. 
With  relatively  small  spans,  the  curve  assumed  by  a  wire 
suspended  between  two  insulators  approximates  with  suf- 
ficient accuracy  to  a  parabola.  On  this  assumption  the  sag 
in  feet  at  the  lowest  probable  temperature  will  be 

°  =  rr  w 

where  w  is  the  resultant  force  in  pounds  per  foot  of  wire 
length,  /  is  the  distance  between  the  supporting  insulators 
on  the  same  horizontal  level  in  feet,  and  T  is  the  maximum 
allowable  tension  in  the  wire  in  pounds  (assumed  uniform 
throughout  the  length  of  the  wire). 
The  length  of  the  wire  in  feet  may  be  expressed  as 

(6) 

If  this  wire  were  removed  from  the  supports  and  laid  on 
the  ground  its  length  would  be 

L»  --  ^'  (7) 


where  Lu  is  the  unstressed  length  of  the  wire  in  feet,  A  is 
the  area  of  the  wire  cross-section  in  square  inches  and  E 
is  the  stretch  modulus  of  elasticity  of  the  wire  material  in 
pounds  per  square  inch. 

Inasmuch  as  wires  are  strung  without  ice-  coverings  and 
usually  in  fair  weather  on  other  than  the  coldest  days,  it  is 


264  TELEGRAPH  ENGINEERING  " 

desirable  to  know  what  sags  to  allow  at  the  higher  tempera- 
tures so  that,  with  the  severest  external  loading  at  lowest 
temperature,  the  tension  will  not  exceed  the  maximum 
allowable  value.  The  increase  of  the  unstressed  length  Lu 
due  to  a  temperature  rise  of  /  fahr.  degrees  above  the  former 
temperature  is  Lukt,  where  k  is  the  temperature  coefficient 
of  linear  expansion  per  fahr.  degree  reckoned  from  the  for- 
mer temperature.  Therefore  the  total  unstressed  length  of 
the  wire  at  the  higher  temperature  will  be 

Lt-L.(i+kt);  (8) 

but  when  strung  its  length  will  be 


where  T1  is  the  tension  of  the  wire  at  the  higher  tem- 
perature. Also  by  analogy  with  equations  (5)  and  (6),  the 
sag  at  this  temperature  is 


do) 
and  the  length  of  the  wire  is 


r        ;j_  (    \ 

Lst=l-\  --  ->  (n) 

3  '     33 

where  w0  is  the  resultant  force  per  foot  of  wire  length  with 
no  ice  covering. 

In  order  to  find  the  sag  Dt  of  the  wire  without  ice  at 
any  temperature  in  terms  of  the  unstressed  length  Lu  at 
the  lowest  temperature,  eliminate  Ltj  L8t  and  Tr  from  equa- 
tions (8)  to  (n),  and  there  results, 


TELEGRAPH   LINES  AND   CABLES  265 

This  cubic  equation  is  of  the  form 

Df  -3  PDt  -2Q  =  o,  (12) 

where  P  =  l-[Lu  (i  +  kt)  -  1}  (13) 

_» 


The  solution  of  equation  (12)  is 

(15) 


when  Pz  >  Q2,  but  when  P3  <  Q*  hyperbolic  cosines  must 
be  used. 

As  an  illustration,  consider  a  No.  9  B.  &  S.  gage  hard- 
drawn  copper  wire  suspended  between  insulators  130  feet 
apart,  the  factor  of  safety  being  taken  as  2.  From  the 

foregoing  table,  T  =  -*-  =315  pounds,  A  =0.01028  square 

inch,  the  wire  diameter  =  0.114  inch  and  the  weight  of 
copper  per  foot  =  0.0396  pound.  The  outer  diameter  of 
an  ice  coating  ^  inch  thick  all  around  the  wire  would  be 
1.114  inch,  and  the  weight  of  this  covering  would  be 

—  X  12  X  0.033  =  0.382  pound  per  foot. 
4 

The  wind  pressure  would  be  -  -  =  0.743  pound  per 

linear  foot.    Whence 


w  =  V(o.o396  +  0.382)2+  (0.743)2  =  0.854, 

and  the  sag  at  the  lowest  temperature  (say  —  20  deg.  fahr.) 
becomes,  from  equation  (5), 


266  TELEGRAPH   ENGINEERING 

The  length  of  the  wire  when  unstressed  is  therefore 


-        —  =  13067,4  =        feet> 
j.  +          315  1-0019 

0.01028  X  16,000,000 
To  iind  the  sag  at  120  deg.  fahr.,  substitute  the  foregoing 

t    T  i//  A\2  /8   XO.II4\2 

value  of  LM,       w0  =  V    0.0396     +    -  -     =  0.0857, 

\  /        \       12       / 

and  /  =  140  in  equations  (13)  and  (14).     Thus, 

P  =  ^p[I3°43  0  +  0.0000095  X  140)  -  130]  =  9.75, 

and 

Q  •_  3  X  130.43  (i  +0.0000095  X  140)  0.0857  (i3o)3  _ 
128  X  0.01028  X  16,000,000 

Since  P3  >  Q2,  the  sag  at  this  temperature,  from  equation 
05)>  is 

/  -        /i  ^  Si 

Dt  =  2  V9«75  cos  (  -  cos"1    , 

\  V- 


3 
=  6.24cos27°47'  =  5.52  feet, 

and  its  vertical  component  is 


For  unusually  long  spans,  such  as  river  crossings,  wire  of 
steel  or  copper-clad  steel  are  more  suitable  than  of  hard- 
drawn  copper  or  galvanized  iron. 

3.  Economical  Span  Length.  —  To  determine  the  pole 
spacing  conducive  to  a  minimum  annual  maintenance 
charge  on  the  supporting  structures  of  an  aerial  line,  let 


TELEGRAPH  LINES  AND   CABLES  267 

n  =  economic  number  of  poles  per  mile, 

h  =  minimum    required    distance    of    wires    above 

ground  in  feet, 

H  =  height  of  pole  above  ground  in  feet, 
Ci  =  cost  of  cross-arms,  insulators  and  pins  per  pole 

in  dollars, 
r  =  average  interest  and  depreciation  rate  on  poles, 

insulators,  etc., 
Wi  =  weight  per  foot  of  wire  in  pounds  at  maximum 

sag, 

T  =  tension  in  conductor  in  pounds  at  maximum  sag, 
and  D'  =  maximum  vertical  sag  in  feet. 

Assume  that  the  cost  of  the  line  wire  will  not  vary 
with  the  pole  spacing,  and  that  the  cost  of  the  poles  ready  to 
set  varies  as  the  square  of  their  height,  or  Cp  =  aH2  dollars, 

where  a  is  a  constant.     Then  the  pole  spacing  is  /  =  -  —  - 

n 

feet,  and  the  height  of  the  poles  is  (see  §  2) 


The  cost  of  line  material  per  mile,  exclusive  of  conductors, 
is 

C  =  n  (Ci  +  Cp)  dollars; 

consequently  the  annual  expense  per  mile  for  maintaining 
the  pole  line  is 


Ca  =  m  |  C,  +  a  [h  +  H  ff9)2]2  j  dollars.      (17) 

To  determine  the  minimum  annual  expense  equate  to  zero 
the  differential  coefficient  of  Ca  with  respect  to  n.    Then 


268  TELEGRAPH  ENGINEERING 

dC*  _  vC  72      arw1h($28o)2      sarw?  (528o)4  _ 

dn~~  4Tn*  64  TV  °' 

or 

4       aWjh&So)2     g        3<m>i2(528o)4  , 

-  *  "  = 


This  equation  is  of  the  form  x2  —  px  —  q  =  o,  and  when  p 
and  q  are  positive  quantities  the  solution  may  be  written 


as  *  =  £  +  y          +  q.     If  w2  =  x, 


(528o)2  ,    , 

' 


and                       q  =  64p(cv:     ..^'  M 

then  


As  an  illustration,  consider  the  following  values  sug- 
gestive of  the  order  of  magnitude  of  the  cost  constants 
for  a  3-arm  24-wire  pole  line  with  poles  6  inches  in  diameter 
at  top: 

a  =  0.006, 
Ci  =  1.50, 
r  =  0.15. 

Then  for  No.  9  B.  &  S.  gage  hard-drawn  copper  wires 
covered  with  ice  J  inch  thick  all  around  and  suspended 
with  a  factor  of  safety  of  3,  at  the  minimum  distance  of 
20  feet  above  the  ground, 

T  =  210  pounds, 
and  wi  =  0.422  pound  per  foot  (page  265). 


TELEGRAPH  LINES   AND   CABLES  269 

For  these  constants 

0.006  X  0.422  X  20  (5280)2 
4  X  210  (1.50  +  0.006  X  2O2) 

3  X  0.006  (0.422)2  (528o)4 

and       q  =  -  —^  =  226,000; 

64  (2io)2  (1.50  +  0.006  X  20 ; 

whence  from  equation  (21)  the  economic  pole  spacing  is 
n  =  V  215  -f  V(2i5)2  +  226,000  =  27  poles  per  mile. 

The  height  of  towers  to  be  used,  and  the  annual  mainte- 
nance of  the  supporting  structure  for  the  wires,  may  now  be 
found  from  equations  (16)  and  (17)  respectively,  yielding 
H  =  29.5  feet  above  ground,  and  Ca  =  27  dollars  per  mile. 

4.  telegraph  Cables. —  Aerial  and  underground  tele- 
graph cables  are  formed  of  any  desired  number  of  annealed 
copper  wires,  from  No.  14  to  No.  19  B.  &  S.  gage,  indi- 
vidually insulated  with  prepared  paper,  fibre  or  sometimes 
rubber.  These  conductors  are  assembled  in  layers,  form- 
ing a  cylindrical  group  or  core  and  held  in  shape  by  one  or 
more  spiral  coverings  of  paper,  and  the  whole  is  then  en- 
closed in  a  lead  sheath  or  else  is  covered  with  tarred  jute 
and  is  surrounded  by  a  cotton  braid  saturated  with  water- 
proof compound.  Lead-covered  paper-insulated  cables  are 
now  principally  used  in  telegraphy,  and  are  called  saturated- 
core  cables  if  the  paper  insulation  is  saturated  with  an  in- 
sulating compound,  or  dry-core  cables  if  the  insulation  is 
untreated.  The  saturated-core  cables  excel  the  dry-core 
cables  in  the  protection  afforded  in  case  of  mechanical 
injury,  but  have  a  higher  electrostatic  capacity,  due  to 
the  larger  specific  inductive  capacity  of  the  insulating  com- 
pound. Low  capacity  is  especially  desired  in  telephonic 


270 


TELEGRAPH   ENGINEERING 


transmission  and  therefore  dry-core  cables  with  somewhat 
smaller  wires  (usually  of  No.  19  to  No.  22  B.  &  S.  gage  for 
local  distances)  are  considered  standard  practice.  In  order 
to  exclude  moisture  from  dry-core  cables,  the  ends  of  sec- 
tions when  supplied  by  manufacturers,  are  always  satu- 
rated with  paraffin  or  other  insulating  compound  for  a 
distance  of  about  two  feet,  and  the  lead  sheath  is  then 
hermetically  sealed.  The  sheaths  for  cables  may  be  of 
pure  lead,  lead  and  antimony  composition,  or  lead  with 
a  small  percentage  of  tin;  their  minimum  thicknesses  are 
outlined  in  the  following  table. 


Number  of 
conductors 

Thickness  of 
sheath 

Inch 

10  tO  100 

Ji- 

IOO  tO  2OO 

/z 

200  tO  400 

A 

The  conductors  of  a  paper-insulated  cable  may  have  a 
single,  double  or  triple  wrap  of  manila  rope  paper  spirally 
applied,  the  thickness  of  each  being  from  0.004  to  0.008 
inch.  The  thickness  of  the  insulation  around  the  con- 
ductors of  a  rubber-insulated  aerial  or  underground  tele- 
graph cable  varies  from  20  to  60  mils. 

Telegraph  companies  usually  specify  that  the  individual 
rubber-insulated  conductors  for  a  telegraph  cable  be  im- 
mersed in  water  for  24  hours  and  thereafter  while  still 
immersed  be  able  to  withstand  an  alternating  electro- 
motive force  of  looo  volts,  applied  for  one  minute  be- 
tween the  conductor  and  the  water.  With  dry-core  cables 
the  finished  lead-covered  cable  is  subjected  to  a  similar 
test.  The  insulation  resistance  of  each  conductor  is  then 


TELEGRAPH  LINES   AND   CABLES 


271 


measured  by  an  application  of  100  volts  for  one  minute 
across  this  conductor  and  all  the  other  wires  and  the 
sheath,  the  reference  temperature  being  60  deg.  fahr.  A 
table  showing  the  variation  of  the  average  insulation  re- 
sistance with  temperature  is  usually  supplied  by  the  cable 
manufacturer. 

Cables  are  also  used  where  telegraph  lines  extend  across 
rivers,  lakes  and  bays,  or  from  the  mainland  to  islands. 
Such  submarine  cables  are  formed  of  either  rubber-  or 
paper-insulated  conductors  within  a  lead  sheath,  this 
sheath  being  covered  with  several  layers  of  jute  thoroughly 
saturated  with  a  waterproof  compound.  Cables  to  be 
installed  on  rocky  river-beds  or  in  waters  having  rapid 
currents  are  provided  in  addition  with  an  armor  of  galva- 
nized iron  wire,  which  is  surrounded  by  jute  servings  sat- 
urated with  a  compound  of  pitch  and  fine  sand. 

The  telegraph  cable  mileage  in  the  United  States  in  1907 
is  tabulated  below: 


Location 

Miles  of  cable 

Miles  of  single 
wire  in  cables 

Average  num- 
ber of  wires  per 
cable 

Overhead 

2  ego 

40,066 

ie    e 

Underground  

1130 

37,727 

33.4 

Submarine* 

7760 

7.7,82 

2    O 

Total  

7488 

8<?,i7<; 

*  Exclusive  of  ocean  cables. 

The  weights  and  prices  of  the  Standard  Underground 
Cable  Company's  telegraph  cables,  composed  of  No.  14 
B.  &  S.  gage  conductors  with  fibre  or  paper  insulation 
measuring  /2  inch  in  diameter  over  insulation,  are  given 
in  the  following  table: 


272 


TELEGRAPH  ENGINEERING 


Number  of 
conductors 

Diameter  over 
sheath  in 
inches 

Weight  in 
pounds  per 
foot 

Catalog  price 
in  cents  per 
foot 

5 

0.76 

I.4I 

25-1 

10 

0.97 

1-93 

33-9 

20 

1.16 

2,.  55 

45-7 

50 

1.63 

4-23 

81.2 

100 

2.18 

6-54 

133-9 

150 

2-55 

8.45 

181.5 

Aerial  Cable  Installation.  —  In  supporting  overhead 
cables  on  pole  lines  it  is  necessary  to  provide  supports  be- 
tween poles  because  the  cable  itself  does  not  possess  suf- 
ficient strength  to  sustain  its  own  weight  over  ordinary 
pole  spans.  The  required  support  is  furnished  by  solid  or 
stranded  galvanized  steel  messenger  wires  of  proper  size,  in 
accordance  with  the  weight  of  the  cable  and  length  of 
span,  to  which  the  cable  is  fastened-  by  means  of  appro- 
priate hangers  at  intervals  of  about  2  feet.  The  messenger 
wire  is  fixed  to  the  sides  of  poles  or  to  their  lower  cross- 
arms  by  means  of  suitable  messenger  supports.  The  sizes 
and  breaking  stresses  of  various  grades  of  steel  messengers 
are  given  in  the  following  table: 


Diameter 

Weight  in 

Breaking  st 

ress  in  pounc 

Is 

in  inches 

pounds  per 
100  feet 

Besse- 
mer 

Siemens- 
Martin 

High- 
strength 

Plow 

Solid  | 

0.192 
0.225 

9.8 
13-4 

.... 

2,500 
3.500 

4,300 
5.900 

6,000 
8,000 

Stranded  • 

0.250 
0.312 
o  37"? 

13.0 
22.0 

30  o 

2,500 
4,200 

r  700 

3,060 
4,860 
6,800 

5,100 
8,100 
1  1  ,  500 

7,600 
12,100 
17,250 

0-437 
0.500 

4O.O 
52.0 

7,600 
9,8OO 

9,000 
1  1  ,000 

15,000 
18,000 

22,500 
27,000 

TELEGRAPH   LINES   AND   CABLES 


273 


The  sags  of  messengers  at  different  temperatures  and 
the  transverse  stresses  on  aerial 
cable  pole  lines  may  be  deter- 
mined in  the  same  manner  as 
shown  in  §  2.  One  type  of  cable 
hanger,  known  as  the  metro- 
politan, is  represented  in  Fig.  6. 


5.  Underground  Cable  In- 
stallation. --In  densely-popu- 
lated localities  it  is  customary  to  place  telegraph  and 


Fig.  6. 


Fig.  7. 


other  electric  cables  underground.     These  cables  are  not 
buried  in  the  ground,  but  are  drawn  into  finished  ducts 


274 


TELEGRAPH   ENGINEERING 


or  conduit  from  one  manhole  to  another.  When  laid, 
conduit  having  a  sufficient  number  of  ducts  to  allow 
for  future  growth  is  placed  in  a  trench  and  is  partially 
or  entirely  surrounded  with  concrete.  Fibre  and  vitrified- 
clay  conduits  are  those  principally  installed,  but  ducts  may 
also  be  formed  in  concrete  directly.  Fig.  7  illustrates  the 
single-duct  and  multiple-duct  types  of  vitrified  clay  con- 
duit manufactured  by  the  H.  B.  Camp  Company.  The 
lengths  of  multiple-duct  conduit  are  held  in  alignment  by 
dowel  pins  and  each  joint  is  wrapped  with  a  layer  of  wet 
muslin  or  burlap  and  thereafter  plastered  with  cement 
mortar.  The  top  of  conduits  should  not  be  less  than  20 
inches  below  the  street  surface. 

The  arrangement  of  a  six-duct  conduit  of  concrete,  fibre, 
multiple-duct  clay  and  single-duct  clay  is  shown  in  Fig.  8, 
with  dimensions  in  inches.  The  total  costs  per  trench 
foot  of  these  types  of  conduit  construction  installed,  in- 
cluding repaving  but  exclusive  of  manholes,  as  estimated 
by  W.  N.  and  C.  L.  Matthews,  for  various  numbers  of 
ducts,  are  given  in  the  following  table: 


Num- 

Costs  per  trench  foot  in  dollars 

ducts 

Concrete 

Fibre 

Multiple 
clay 

Single 
clay 

I 

O  44 

°  51 

2 

0.56 

0.67 

0-73 

0.76 

3 

0-73 

0.88 

1.03 

1.05 

4 

0.83 

0.91 

0.98 

1.09 

6 

0.97 

1.22 

1-37 

1  .46 

8 

I.I7 

i-SS 

1.64 

1.92 

12 

1  .40 

1.98 

2.  II 

2.45 

16 

l.67 

2.42 

2.72 

3.01 

20 

I-9S 

2.94 

3-22 

3563 

TELEGRAPH  LINES  AND   CABLES 


275 


This  table  is  based  upon  the  spacings  shown  in  Fig.  8, 
but  with  multiple-duct  vitreous  clay  conduit  i  inch  of 
concrete  is  allowed  between  the  sections,  and  it  assumes 
that  the  conduit  is  laid  in  streets  with  granite  or  equivalent 
paving.  Oftentimes  the  concrete  at  the  sides  of  the  con- 


4. 


m 


f!X      4>U      •O'l  »I t£?.: 

I3CK1 

.--.• 


FIBRE  TUBE 


MULTIPLE  CLAY 


Fig.  8. 


duit  is  dispensed  with,  thereby  reducing  the  cost  of  in- 
stallation. 

Manholes,  or  conduit-openings,  are  located  along  the 
conduit  line  at  suitable  distances  apart,  rarely  greater  than 
700  feet,  to  facilitate  the  installation,  repair  and  removal 
of  cable  sections.  The  manholes  are  constructed  of  brick 
or  concrete,  in  sizes  of  3  ft.  by  3  ft.  and  upwards,  depend- 
ing on  the  number  of  cables  to  be  accommodated.  Fig.  9 


276 


TELEGRAPH  ENGINEERING 


shows  a  section  of  an  oval  manhole  whose  inside  dimen- 
sions are  7  ft.  by  3!  ft.  The  costs  of  manholes  of  either 
construction  vary  from  about  $60  to  $150  according  to 
their  size  and  the  nature  of  the  ground  where  they  are 
installed. 


GRADE  LINE  \ 


Fig.  9. 

Cable  Splices.  —  Aerial  and  underground  cables  are  al- 
most invariably  spliced  near  poles  or  in  manholes  respec- 
tively. The  method  of  making  splices  in  multi-conductor 
paper-insulated  cables  is  indicated  in  Fig.  10.  Two  cables 
to  be  spliced  are  placed  in  position  so  that  their  conductors 
overlap  from  12  to  24  inches,  depending  on  the  number  of 
conductors.  The  corresponding  innermost  conductors  of 
the  two  cables  are  then  twisted  together  as  shown  at  A, 
and  a  paper  or  cotton  tube  is  placed  over  the  joint  as 
shown  at  B.  All  others  are  similarly  spliced  with  the 
joints  staggered  (C,  Fig.  10),  and  then  the  entire  splice 
is  boiled  out  with  paraffin  and  wrapped  with  muslin  or 
linen.  A  lead  sleeve,  whose  inside  diameter  exceeds  the 


TELEGRAPH  LINES  AND   CABLES 


277 


outside  diameter  of  the  cable  sheaths  by  i  or  i|  inches, 
is  then  placed  over  the  splice  and  is  joined  to  the  sheath 
by  means  of  wiped  soldered  joints. 


Fig.  10. 

Cable  Pole  Boxes.  —  At  suburban  points  beyond  which  it 
is  not  deemed  necessary  to  extend  underground  cable  lines, 
and  at  water  crossings,  cables  are  brought  to  the  tops  of 
poles  and  terminated  in  cable  pole  boxes,  as  shown  in  Fig. 
ii.  Combined  fuses  and  lightning  arresters  are  located 
within  this  cable  box,  as  shown  at  /,  and  are  interposed 
between  the  bare  aerial  wires  and  the  cable  conductors. 

Electrolysis  of  Underground  Cable  Sheaths.  —  If  stray 
electric  currents  of  an  electric  railway  system,  in  wending 
their  way  back  to  the  generating  station,  flow  out  of  cable 
sheaths  in  moist  locations  at  certain  places,  electrolytic  de- 
composition of  the  sheaths  occurs  at  these  places,  for  the 
sheaths  there  behave  as  anodes  in  electrolytic  cells.  Con- 
tinued electrolytic  decomposition,  or  electrolysis,  causes 
the  pitting  of  the  cable  sheath,  and  the  consequent  ad- 
mission of  moisture  to  the  insulation  around  the  con- 
ductors within  the  protecting  sheath.  The  extent  of 


278 


TELEGRAPH  ENGINEERING 


electrolysis  depends  upon  the  number  of  ampere-hours 
conducted,  since,  according  to  t  araday's  Law,  one  ampere 
flowing  out  of  a  lead  sheath  into  an  electrolyte  for  one  hour 
would  dissolve  3.87  grams  of  lead. 


Fig.  ii. 

In  order  to  locate  the  regions  where  this  rapid  corrosion 
of  cable  sheaths  takes  place,  tests  are  made  at  manholes 
to  determine  the  potentials  of  the  sheaths  with  respect  to 
the  adjacent  ground,  and  the  amounts  of  current  carried 
by  them.  By  thus  observing  the  direction  and  value  of 
the  stray  currents  at  a  number  of  manholes,  the  places 
where  currents  leave  the  cables  and  pass  to  the  moist 
ground  are  readily  determined.  Where  a  cable  sheath  is 
found  by  test  to  be  decidedly  positive  with  respect  to 


TELEGRAPH  LINES  AND   CABLES  279 

ground  or  to  the  railway  track,  a  temporary  connection  of 
heavy  copper  wire  including  an  ammeter  may  be  made 
from  the  sheath  to  a  suitable  ground,  to  the  track,  or  to 
a  neighboring  negative  feeder.  Readings  at  other  places 
where  the  sheath  was  positive  to  earth  may  then  be  re- 
peated, and  if  conditions  are  improved,  a  permanent 
soldered  bond  is  installed  so  that  the  current  may  flow 
from  the  cable  along  a  wire  instead  of  into  an  electrolyte. 
Where  several  cables  pass  through  a  manhole  it  is  good 
practice  to  bond  all  of  them  together.  After  such  bonds 
are  in  place,  another  complete  and  final  survey  is  made. 
The  use  of  negative  track  feeders  of  proper  copper  dis- 
position, and  possibly  with  negative  boosters  in  these 
feeders,  reduces  the  stray  railway  currents  to  a  large 
extent.* 

6.  The  Earth  as  a  Return  Path.  —  Professor  Steinheil 
in  1837  made  the  discovery  that  the  earth  may  be  used  as 
a  portion  of  an  electric  circuit.  It  has  been  stated  that 
the  resistance  of  the  earth  when  used  as  a  return  circuit 
for  a  telegraph  line  is  very  small  if  the  line  terminals  are 
properly  grounded.  To  verify  this  statement,  consider  a 
hemispherical  ground  electrode  of  radius  a  centimeters  to 
be  buried  a  short  distance  below  the  earth's  surface.  The 
resistance  of  the  earth  outward  from  this  electrode  to  a 
distance  d  centimeters  is 

pdr  xv 


-£ 


as  expressed  by  Heaviside,  where  p  is  the  specific  resist- 
ance of  the  earth,  assumed  uniform,  in  ohms  per  centi- 

*  See   Sheldon  &  Hausmann's  "Electric  Traction  and  Transmission 
Engineering,"  p.  157;  G.  I.  Rhodes'  paper,  A.I.E.E.,  Trans.  1907,  p.  247. 


280 


TELEGRAPH   ENGINEERING 


meter  cube,  and  r  and  r  +  dr  are  the  radii  of  concentric 
hemispherical  equipotential  surfaces,  in  centimeters.  The 
distribution  of  resistance  outward  from  this  electrode  may 
be  calculated  from  equation  (22)  by  considering  the  resist- 
ances over  the  distances,  say  a  to  2  a,  2  a  to  4  a,  and  so  on. 
Thus 


2irJa 
P 


871-0 


ohms,  etc. 


The  following  table  shows  the  resistance  values  for  the 
various  distances  from  the  electrode,  and  Fig.  12  shows 
the  total  resistance  outward  from  the  electrode  for  a  par- 
ticular case  in  which  p  =  800  ohms  per  centimeter  cube  and 
a  =  i  foot  =  30.5  centimeters. 


Distance  in 
centimeters 

Resistance 
in  ohms 

a  to  2  a 

o  .  07958  p/a 

2  a  to  4  a 

o.  03979  p/a 

4  a  to  8  a 

0.01989  p/a 

8  a  to  16  a 

0.00994  p/a 

16  a  to  32  a 

0.0049  7  p/a 

32  a  to  64  a 

0.00248  p/a 

64  a  to  128  a 

0.00124  P/a 

It  is  seen  that  the  greater  share  of  the  ground  resistance 
is  very  near  the  electrode,  consequently  good  conductivity 
of  the  soil  near  the  electrode  is  essential,  but  with  greater 
distances  from  the  electrode  the  earth's  conductivity  be- 
comes of  less  importance.  It  is  also  to  be  noted  that  the 
resistance  varies  inversely  with  the  size  of  the  electrode, 
whence  the  desirability  of  utilizing  available  extensive 
municipal  water  pipes  as  ground  electrodes. 


TELEGRAPH*  LINES  AND   CABLES 


28l 


Inasmuch  as  the  resistance  between  two  electrodes  is 
principally  in  the  neighborhood  of  these  electrodes,  the 
total  resistance  between  them  might  be  expressed  as 


2  7T 


(23) 


20  40  60  80 

DISTANCE  FROM  GROUND 

ELECTRODE  IN  FEET 

Fig.  12. 


where  a  and  a'  are  the  radii  of  the  two  electrodes  respec- 

tively, it  being  understood  that  one  electrode  is  not  perfectly 

insulated  from  its  mate.     Some  instances  of  almost  com- 

plete   electrical    isolation 

of  the  ground  at  a  local- 

ity from  the  earth  have 

been  observed.     Thus,  to 

secure    telegraphic    com- 

munication   with    Nash- 

ville, Tenn.,  it  was  found 

necessary    to    extend    a 

ground-wire     from     that 

city  to  an  effective  ground 

at  a  point  several  miles  distant.     On  the  other  hand,  large 

sections  of  the  earth  between  two  widely-separated  stations 

may  be  perfectly  insulating  without  materially  increasing 

the  resistance  of  the  ground  return. 

When  the  pipes  of  a  community's  water  supply  are  not 
available  as  a  ground  electrode,  satisfactory  ground  con- 
nections may  be  made  by  driving  two  or  more  iron  pipes 
about  2  inches  in  diameter  into  moist  earth  in  the  basement 
of  the  telegraph  office.  Line  and  office  connections  with 
such  pipe  grounds  are  of  copper  wire,  usually  larger  than 
No.  9  B.  &  S.  gage,  well  soldered  to  the  pipes. 

In  the  practical  measurement  of  ground  resistance  either 
another  permanent  electrode  presenting  a  known  ground 


282  TELEGRAPH  ENGINEERING 

resistance  or  two  auxiliary  temporary  ground  electrodes 
or  grounds  are  used,  these  test  grounds  being  at  least  15 
feet  distant  from  each  other  and  from  the  permanent 
main  ground  whose  resistance  is  to  be  measured.  In  the 
first  case  the  series  resistance  of  the  two  grounds  minus 
the  resistance  of  the  known  ground  gives  to  a  fair  degree 
of  accuracy  the  resistance  of  the  desired  ground.  In  the 
second  case,  employing  two  auxiliary  grounds  in  the 
measurement  of  the  main  ground,  the  resistance  between 
each  pair  is  observed.  Then,  if  RI  be  the  series  resistance 
between  the  main  and  first  auxiliary  grounds,  R%  that 
between  the  main  and  second  auxiliary  grounds  and  RZ 
that  between  the  two  auxiliary  grounds,  it  follows  that 
the  earth  resistance  at  the  main  ground  is 

R  =  *i  +  fr-ft.  (24) 

2 

The  resistance  of  a  ground  will  vary  from  time  to  time,  de- 
pending upon  the  amount  of  moisture  in  the  soil  in  the 
immediate  neighborhood  of  the  electrode.  In  practice 
these  resistance  measurements  are  made  periodically,  at 
least  once  a  year. 

The  Western  Union  Telegraph  Company  specifies  that 
the  resistances  of  various  classes  of  grounds  should  not  in 
general  exceed  the  following  values: 

Central  office  battery  grounds o .  i  ohm, 

Small  office  and  test  station  grounds 5  ohms, 

Lightning  arrester  grounds 15  ohms, 

High-potential  protection  grounds 25-100  ohms. 

7.  Electrical  Constants  of  Telegraph  Conductors.  —  The 
four  electrical  constants  of  a  line  conductor  are :  resistance, 
inductance,  capacity  and  leakance. 


TELEGRAPH  LINES  AND   CABLES  283 

Resistance.  —  The  resistance  to  direct  currents  of  a  wire 
of  area  A  square  inches,  at  any  temperature  /  degrees  cent., 
expressed  in  ohms  per  mile,  is 

R  =  0.02495  .£  (i  +  at),  (25) 

where  p  is  the  specific  resistance  in  microhms  per  centi- 
meter cube  of  the  material  at  o°cent.,  and  a  is  the  mean 
temperature  coefficient  of  electrical  resistance  per  centi- 
grade degree  reckoned  from  o°  cent.  Accepted  values  of 
these  constants  for  copper  and  iron  follow: 


Material 

P 

a 

Annealed  copper  (stand.) 
Hard-drawn  copper  
Galvanized  iron  

1.587 
1.631 
9.69 

0.00427 
O.OO4I4 
0.0058 

Tabulated  values  of  the  resistances  of  standard  sizes  of 
telegraph  wire  are  given  in  Chap.  I.  The  conductivity  of 
commercial  copper  and  bimetallic  wire  is  usually  specified 
as  a  percentage  of  that  of  standard  annealed  copper. 

Inductance.  —  The  self-inductance  of  a  single  linear  cylin- 
drical wire,  mounted  at  a  height  h  above  the  ground  which 
serves  as  the  return  path,  is 

.   r. 

L  =  0.000741  logio  ^  +  0.0000805  n  (26) 

henrys  per  mile,  where  D  is  the  diameter  of  the  conductor 
and  p.  is  its  permeability.  A  short  table  of  logarithms 
appears  in  the  appendix.  The  mutual  inductance  between 
two  parallel  ground-return  wires,  mounted  at  the  same 
height  above  the  ground  and  separated  by  a  distance  d,  in 
henrys  per  mile,  is 


,,  ,    N 

M  =  0.000741  logio  -  *—  ---  (27) 


284 


TELEGRAPH  ENGINEERING 


In  these  expressions,  h,  D  and  d  must  be  expressed  in  the 
same  units.  Therefore  the  total  inductance  of  the  two 
similar  wires  for  equal  currents  in  the  same  direction  is 

L.  =  i(L  +  aO,  (28) 

while  for  equal  currents  in  opposite  directions  is 


2  d 
or     0.00148:2  logio— 


0.000161  ju.   (29) 


Equation  (29)  indicates  that  the  inductance  of  wires 
within  a  grounded  conducting  sheath  is  very  small,  inas- 
much as  the  sheath,  which  may  be  considered  as  the  return 
path,  is  very  near  the  conductors. 

For  compound  conductors  consisting  of  a  steel  core  sur- 
rounded by  a  copper  shell,  the  factor  /z  in  the  foregoing 
equations  is  replaced  by  the  values  given  in  the  following 
table  for  various  ratios  n  of  the  conductivity  of  the  com- 
pound wire  to  that  of  a  solid  copper  wire  of  the  same 
outside  diameter,  //  being  the  permeability  of  the  steel  core. 


n 

Factor  to  replace  n 

O.  2 

0-3 
0.4 

o-5 

o.2g8fjLf    +0.1292 
o.  1012/1'  +  o.  204 
0.0416  M'  +  o.  294 
o.  0185  M'  +  0.386 

This  table,  derived  from  that  given  by  Fowle,*  assumes 
steel  to  have  12  per  cent  of  the  conductivity  of  copper. 

Capacity.  —  The    capacity   of   a   single   overhead   wire 
utilizing  ground  as  its  return,  in  microfarads  per  mile,  is 


C  = 


0.0894 


,t 


(3°) 


cosh"1 


*  Electrical  World,  v.  56,  p.  1474. 

f  Sheldon  and  Hausmann's  "  Electric  Traction  and  Transmission  Engi- 
neering," p.  230. 


TELEGRAPH  LINES  AND   CABLES  285 

the  symbols  having  the  same  significance  as  above.  For 
large  values  ot  — ,  it  is  more  convenient  to  use  the  very 
approximate  equation 


where  €  is  the  base  of  Napierian  logarithms  and  is  equal  to 
2.7183.  Logarithms  to  the  base  e  may  be  obtained  by  mul- 
tiplying the  corresponding  logarithms  to  the  base  10  by 
2.3026;  that  is,  logex=  2.3026  logio  %> 

When  a  number  of  overhead  wires  are  located  near  each 
other,  the  capacity  of  each  wire  is  increased  by  the  pres- 
ence of  the  others.  For  two  parallel  ground-return  wires 
suspended  at  the  same  height  above  the  ground  and  sepa- 
rated a  distance  d  from  each  other,  Heaviside  gives  as  the 
capacity  of  each  wire  in  microfarads  per  mile: 

0.0894  log^  -=- 

(a*) 


Their  mutual  capacity  in  microfarads  per  mile  is 
0.0894  log€ 


As  the  number  of  wires  in  close  proximity  to  each  other 
increases,   the  formulae  for  their  individual  and  mutual 

*  Sheldon  and  Hausmann's  "  Alternating  Current  Machines,"  p.  313. 


286  TELEGRAPH  ENGINEERING 

capacities  become  more  and  more  unwieldy  for  numerical 
computation.* 

•  Thus,  for  a  single  No.  9  B.  &  S.  gage  wire,  suspended  25 
feet  above  the  ground,  the  capacity  is 

n  0.0894 


2.3026  log10 


0.00966  mf.  per  mile. 


O.II44 


If   another   similar   ground-return   wire   be   placed   hori- 
zontally i  foot  distant  from  the  first,  then 


A     , 
=  9.25     and     loge  -  '—^L  -  =  3.91; 

therefore  the  capacity  of  each  wire,   as  obtained  from 
equation  (32),  is  now 

„  0.0894  X  9.25  or  M 

C  =  -  --  XV     /       NO  =  0.01178  mf.  per  mile. 
(9.25)2-  (3.91)2 

The  mutual  capacity  of  the  wires  is  found  to  be 
Cm  =  0.0050  mf.  per  mile. 

The  capacity  of  a  single-conductor  cable  within  a  con- 
centric metallic  sheath,  in  microfarads  per  mile,  is 

;.  (34) 


where  k  is  the  specific  inductive  capacity  or  permittivity 
of  the  homogeneous  separating  medium  or  dielectric,  d  is 
the  inside  diameter  of  the  conducting  sheath  and  D  is  the 
diameter  of  the  conductor.  If  the  dielectric  consists  of  n 

*  Refer  to  Oliver  Heaviside,  "Collected  Papers,"  v.  i,  p.  45;    Louis 
Cohen  "  Calculation  of  Alternating  Current  Problems,"  p.  97. 


TELEGRAPH  LINES  AND   CABLES 


287 


cylindrical  layers  having  different  specific  capacities  fe, 
&2,  •  •  •  ,  kn,  and  of  outer  diameters  dit  d%,  .  .  .  d  respec- 
tively, the  capacity  of  the  conductor  in  microfarads  per 
mile  is 


C  = 


0.0894 


D 


d 


(35) 


The  capacity  of  multi-conductor  dry-core  paper-insulated 
aerial  or  underground  cables,  in  microfarads  per  mile,  are 
usually  as  follows: 


B.  &  S.  gage  number 

Mutual  capacity 

Grounded  capacity 

| 

14 

O.  IOO 

Telegraph  cables                  < 

16 

O   OQ2 

* 

18 

O.O8O 

Telephone  cables  \ 

13 

16 

O.O72 
O.O72 

0.108 
0.108 

iQ 

22 

o  .  074-0  .  080 

0.070-0.083 

O.III-O.I2O 
O.IOS-O.I25 

The  mutual  capacity  is  that  of  a  conductor  with  respect 
to  its  mate  of  a  twisted  pair,  all  the  other  wires  being 
grounded  to  the  sheath.  The  grounded  capacity  is  that  of 
one  wire  against  all  the  others  grounded  to  the  sheath. 

Leakance.  —  The  reciprocal  of  the  insulation  resistance 
of  a  line,  when  expressed  in  ohms,  is  called  the  leakage  con- 
ductance or  leakance  of  the  line  and  this  constant  may  be 
expressed  in  terms  of  a  unit  which  is  often  called  the  mho. 

The  insulation  resistance  of  a  well-constructed  open  line 
fastened  to  insulators  that  are  mounted  on  poles  or  towers 
may  be  from  about  50  to  100  megohms  per  mile  in  clear 
weather,  but  will  drop  to  a  fraction  of  a  megohm  during 


288  TELEGRAPH   ENGINEERING 

prevailing  wet  and  foggy  weather.  Thus,  the  leakance  of 
the  wire  at  insulators,  at  places  where  the  wire  touches 
trees,  etc.,  due  to  moisture  and  dirt,  is  of  the  order  of 
from  io~5  to  io~8  mhos. 

The  insulation  resistance  of  a  rubber-  or  paper-insulated 
wire  within  a  sheathed  cable  is  usually  over  200  megohms 
per  mile  (at  60°  fahr.)  when  laid,  spliced  and  connected 
to  terminals,  each  wire  being  measured  against  all  the 
rest  and  the  sheath.  Submarine  cables  generally  have  an 
insulation  resistance  of  over  1000  megohms  per  mile.  The 
leakance  of  a  properly-installed  cable  is  not  affected  by 
weather  conditions  unless  moisture  enters  as  the  result  of 
mechanical  injury  to  the  cable  sheath. 

8.  Elimination  of  Inductive  Interferences  on  Telegraph 
and  Telephone  Lines.  —  Whenever  direct  currents  are 
established,  changed  in  intensity  and  stopped,  or  when- 
ever alternating  currents  are  maintained,  in  an  electric 
circuit,  electromotive  forces  are  induced  in  all  neighboring 
conductors  (a)  due  to  the  varying  magnetic  field,  the  in- 
duced voltages  being  dependent  upon  the  time-rate  of 
change  of  current  in  the  inducing  circuit  and  the  proximity 
of  the  wires  to  this  circuit,  and  (b)  due  to  the  varying 
electrostatic  field,  the  resulting  current  flow  being  depend- 
ent upon  the  time-rate  of  change  of  voltage  in  the  inducing 
circuit  and  the  proximity  of  the  wires  to  this  circuit. 
Thus,  when  telegraph  and  telephone  circuits  are  located 
in  parallel  proximity  to  the  lines  of  large  alternating- 
current  railway  and  power-transmission  systems,  the 
latter  operating  at  voltages  up  to  150,000  volts,  these 
circuits  derive  by  electromagnetic  and  electrostatic  in- 
duction sufficient  voltages  to  interfere  seriously  with  their 


TELEGRAPH  LINES  AND   CABLES  289 

proper  transmission  of  signals.  Fig.  13  shows  the  disturb- 
ing effect  on  a  ground-return  telegraph  line  AB  during  the 
brief  time  that  the  alternating  current  in  the  disturbing 
wire  CD  is  growing  from  zero  to  its  positive  maximum 
value,  the  full  and  dotted  arrows  on  the  telegraph  line  in- 
dicating respectively  the  currents  produced  electromag- 


Fig.  13. 


netically  and  electrostatically.  The  directions  of  these 
currents  change  repeatedly  in  unison  with  the  current  in 
the  disturbing  wire.  With  metallic  circuits  having  the  out- 
going and  return  conductors  close  together,  which  is  the 
almost  universal  arrangement  of  telephone  lines,  electro- 
magnetic disturbances  may  be  eliminated  so  far  as  the 
terminals  are  concerned  by  transposing  the  two  wires  of 
the  telephone  line  at  the  center  of  exposure  to  the  dis- 


Ao" 


Fig.  14. 

turbing  wire,  as  shown  in  Fig.  14,  for  the  same  conditions 
as  in  the  preceding  figure.  However,  electrostatic  dis- 
turbances, while  reduced,  are  not  eliminated,  but  it  is 
evident  that  such  disturbances  may  be  minimized  by  fre- 
quent transposition  of  the  two-line  wires.  When  numer- 
ous aerial  telephone  lines  are  mounted  on  the  same  poles  a 
careful  consideration  will  yield  a  satisfactory  arrangement 
of  transpositions  for  the  elimination  of  mutual  disturbances 


290 


TELEGRAPH  ENGINEERING 


as  well  as  those  occasioned  by  adjoining  power  circuits. 
Fig.  15  shows  a  single  aerial  transposition  made  at  a  trans- 
position insulator  of  the  type  represented  at  the  right  of 
Fig.  i. 

Simple  expedients  for  the  elimination  of  small  inductive 
interferences  on  earth-return  telegraph  lines  have  been  de- 


Fig.  15. 

vised  and  usually  involve:  the  addition  of  inductance  and 
resistance  to  the  line,  shunting  of  relays  with  resistances  or 
condensers,  or  the  provision  on  each  relay  of  a  neutralizing 
winding  which  connects  with  one  coil  of  a  transformer 
whose  other  coil  is  inserted  in  the  line  wire.  Severe  in- 
ductive disturbances  on  grounded  lines,  however,  require 
better  neutralization.  Conductors  within  metallic  sheaths 

are  shielded  from  electrostatic 
but  not  from  electromagnetic 
induction. 

Fig.  1 6  indicates  one  method 
for  diminishing  electrostatic 
and  electromagnetic  disturb- 
ances on  a  ground-return  line. 
At  frequent  intervals  along  the  line  one  coil  of  current 
transformers  S  is  bridged  across  a  resistance  R  in  the 
telegraph  line  AB,  the  other  coil  being  properly  joined 
in  series  with  a  neutralizing  wire  NN,  or,  if  practicable, 
with  the  disturbing  wire  itself.  „  Also  a  potential  trans- 
former P  has  one  coil  included  in  the  neutralizing  wire, 
and  its  other  coil  with  a  condenser  C  of  proper  capacity  is 


Fig.  16. 


TELEGRAPH   LINES  AND   CABLES  2QI 

bridged  from  the  telegraph  wire  to  ground.  This"neutraliz- 
ing  wire  is  placed  parallel  and  close  to  the  telegraph  line 
or  lines  and  inasmuch  as  it  is  subject  to  the  same  magnetic 
effects  as  the  signal  wires,  the  currents  developed  in  it  are 
arranged  to  oppose  by  transformer  action  those  developed 
in  the  telegraph  lines,  thereby  neutralizing  electromagnetic 
disturbance.  Electrostatic  induction  is  neutralized  by  the 
potential  transformer  P  in  a  similar  manner. 

Another  method  *  particularly  suitable  for  single-phase 
alternating-current  railway  systems  and  not  requiring  an 
additional  conductor  is  shown  in  Fig.  17.  The  telegraph 


Fig.  17. 

wire  AB  parallels  the  sectionalized  overhead  trolley  wire 
which  has  alternate  sections  of  opposite  polarity,  as  indi- 
cated, in  order  to  minimize  electrostatic  induction.  Each 
section  is  fed  at  both  ends  from  adjacent  substations  by 
.means  of  the  secondary  windings  s  of  the  transformers 
T,  whose  primary  windings  p  are  connected  across  the 
high-tension  transmission  line,  not  shown.  A  car  located 
between  substations  draws  some  current  from  each  sub- 
station depending  upon  its  distance  therefrom,  and  these 
currents  flow  in  opposite  directions,  the  greater  current 
over  the  shorter  distance,  and  vice  versa.  Electromagnetic 
induction  is  neutralized  by  this  arrangement. 

The   present   method   of   overcoming   the    detrimental 

*  Taylor's  "  Telegraph  and  Telephone  Systems  as  Affected  by  Alternating- 
current  Lines,"  Trans.  A.I.E.E.,  v.  28,  p.  1202. 


2Q2 


TELEGRAPH  ENGINEERING 


effects  of  induction  on  the  telegraph  and  telephone  lines 
paralleling  the  single-phase  lines  of  the  New  York,  New 
Haven  &  Hartford  Railroad,  recommended  by  a  com- 
mittee including  Mr.  G.  M.  Yorke,  is  giving  marked  satis- 
faction in  practical  operation.  The  generator  voltage  of 
11,000  volts  is  stepped  up  to  22,000  volts  by  means  of 
auto- transformers  A,  Fig.  18,  situated  in  the  power  station; 


Fig.  18. 


one  terminal  of  each  transformer  joins  with  the  contact 
conductors  or  trolleys,  the  other  joins  with  feeders  which 
extend  along  the  roadway,  and  the  mid-point  connects  to 
the  rails.  The  arrangement  is  similar  to  three-wire  direct- 
current  distribution  systems  except  that  the  direct  load  is 
on  one  side  of  the  circuit,  the  other  side  receiving  its  share 
through  the  sectionalizing  auto-transformers  T,  T  situated 
on  sectionalizing  bridges  at  frequent  intervals  over  the 
roadway.  It  will  be  seen  that  any  train  draws  its  current 
from  the  auto- transformers  on  either  side,  the  directions 
of  the  currents  in  the  n,ooo-volt  and  2 2,000- volt  circuits 
being  indicated  by  full  and  dotted  arrows  respectively. 
Inasmuch  as  the  two  parts  of  the  current  taken  by  a  train 
flow  in  opposite  directions  toward  this  train,  electromag- 
netic effects  on  adjacent  telegraph  and  telephone  lines  are 


TELEGRAPH   LINES  AND   CABLES 


293 


neutralized.  Since  the  feeders  may  be  placed  in  the  same 
general  direction  as  the  contact  conductors  with  respect 
to  neighboring  lines,  electrostatic  disturbances  may  also 
be  neutralized,  although  such  disturbances  were  inap- 
preciable along  the  electrified  zone  of  the  New  Haven 
Railroad. 


9.  Simultaneous  Use  of  Lines  for  Telegraphy  and  Teleph- 
ony. —  A  pair  of  line  wires  forming  a  metallic  telephone 
circuit  may  be  utilized  at  the  same  time  as  one  or  two 
ground-return  telegraph  lines,  without  interference  be- 
tween the  two  classes  of  service.  A  single  telegraph  line 
may  also  be  used  simultaneously  as  a  grounded  telephone 


SUBSCRIBER  1 


SUBSCRIBER  2 


Fig.  19. 


COMMON-BATTERY  TELEPHONE 

CB 


line.     Such  combined  working  is  extensively  employed  for 
gaining  increased  earning  capacity  of  the  wire  plant. 

Telephone  Circuits.  —  Figs.  19  and  20  show  respectively 
the  connections  of  the  telephonic  apparatus  for  the  inter- 
communication of  two  subscribers  joined  to  a  magneto  and 
a  common-battery  telephone  system.  Sound  waves  imping- 


294  TELEGRAPH   ENGINEERING 

ing  upon  the  diaphragm  of  a  telephone  transmitter  vary 
its  electrical  resistance  and  consequently  vary  the  current 
in  the  corresponding  line  circuit;  the  varying  current  flow- 
ing through  the  magnet  of  the  telephone  receiver  produces 
a  varying  attraction  for  the  iron  diaphragm,  the  motions  of 
which  set  up  sound  waves  in  the  air  which  are  similar  to 
those  incident  on  the  transmitter  diaphragm. 

Each  subscriber's  set  of  a  magneto  telephone  consists 
of  a  telephone  transmitter  T,  telephone  receiver  R,  hand- 
driven  magneto  or  alternating-current  generator  G  (open- 
circuited  normally),  polarized  bell  P,  induction  coil  /,  local 
battery  B  and  receiver  hook  switch  H.  A  subscriber's  set 
of  a  common-battery  exchange  does  not  include  a  gener- 
ator and  local  battery,  but  has  a  condenser  C  which  keeps 
the  set  open-circuited  to  direct  current  when  not  in  use; 
the  circuit  for  such  current  is  closed  by  the  hook  switch 
when  the  receiver  is  lifted  therefrom  in  the  act  of  calling 
and  when  conversing  with  another  subscriber.  Electrical 
energy  for  the  operation  of  the  common-battery  telephone 
circuit  is  supplied  by  the  battery  CB  located  at  the  central 
office,  this  battery  also  supplying  current  to  numerous 
other  similar  circuits,  each  circuit  having  its  own  repeat- 
ing coil  5.  The  apparatus  at  the  central  office  used  in  the 
establishment  and  in  the  supervision  of  the  connection  be- 
tween the  two  subscribers  is  not  shown  in  the  figure. 

The  repeating  coil  S  is  similar  in  design  to  the  retarda- 
tion coils  used  with  the  bridge  duplex  telegraph  circuits 
(p.  71),  except  that  the  resistance  of  each  of  the  four 
windings  is  usually  from  20  to  40  ohms.  Coils  b  and  c 
form  the  primary  winding,  and  coils  a  and  d  form  the 
secondary  winding  of  a  transformer  when  subscriber  i  is 
talking,  the  reverse  being  true  when  subscriber  2  is  talking. 


TELEGRAPH   LINES  AND   CABLES  295 

Variations  in  current  magnitude  in  one  subscriber's  circuit 
are  thus  inductively  transferred  to  the  circuit  of  the  other 
subscriber. 

Simplex  Signalling  over  Telephone  Lines.  —  The  simplex 
simultaneous  signalling  system  affords  the  transmission  of 
one  telephone  and  one  telegraph  message  over  one  pair  of 
wires,  as  indicated  in  Fig.  21.  The  two  wires  are  used  as 


TO  CENTRAL JVV-^O  °fr~^<\_  T°  CENTRAL 

OFFICE  OF  CTT    S    Ifa 1  1 LTT    S    ID    OFFICE  OF 

SUBSCRIBER    1    X>-O/d  JC^X/T  SUBSCRIBER  2 


Fig.  21. 

a  metallic  telephone  circuit,  and  both  wires  in  parallel  are 
used  as  the  line  wire  of  a  ground-return  telegraph  line. 
The  junctions  between  the  coils  b  and  d  of  the  two  re- 
peating coils  5,5  connect  with  the  usual  telegraphic  ap- 
paratus at  single  Morse  stations.  When  the  lines  and 
repeating  coils  are  properly  balanced,  the  current  for 
actuating  the  telegraph  relays  divides  equally  between  the 
two-line  wires  in  flowing  from  station  B  to  A,  and  these 
portions  flow  in  opposite  directions  around  the  iron  cores 
of  the  repeating  coils,  thereby  contributing  no  magnetiza- 
tion to  the  cores.  Consequently  the  telegraph  currents 
will  not  affect  the  telephone  instruments  which  connect 
with  the  repeating  coil  windings  a  and  c.  Inasmuch  as 
the  points  of  attachment  of  the  telegraphic  apparatus  are 
neutral  points  of  the  telephone  line,  the  telephone  voice  and 
ringing  currents  will  not  affect  the  telegraph  relays.  The 
simultaneous  transmission  of  both  messages  is  improved 


296 


TELEGRAPH   ENGINEERING 


by  the  shunting  of  condensers  C  around  the  key  contacts. 
It  is  evident  that  the  resistance  of  the  telegraph  line  cir- 
cuit is  only  half  that  of  one  of  the  telephone  lines. 

Intermediate  telegraph  stations  may  be  readily  intro- 
duced into  the  circuit  of  Fig.  21  by  inserting  two  retardation 
coils  and  joining  the  mid-points  of  their  coils  to  the  tele- 
graph apparatus  at  the  intermediate  office. 

In  telephony,  an  extension  of  the  circuit  arrangement, 
shown  in  Fig.  2 1 ,  whereby  two  telephone  circuits  each  with 
two  repeating  coils  permit  of  the  establishment  of  a  third 
telephone  circuit,  is  much  used  for  long-distance  trans- 
mission. This  third,  or  so-called  phantom  circuit,  utilizes 
the  two  conductors  of  one  of  the  side  or  physical  circuits 
as  the  outgoing  conductor,  and  the  two  conductors  of  the 
other  physical  circuit  as  the  return  (see  Fig.  24),  with  an 
obvious  gain  in  transmission  efficiency. 


TO          R 
TELEPHONE 
APPARATUS  R 


Fig.  32. 

Composite  Signalling.  —  Composite  simultaneous  signal- 
ling secures  the  transmission  of  one  telephone  and  two 
telegraph  messages  over  one  pair  of  wires,  each  telephone 
wire  serving  as  a  ground-return  telegraph  line.  Pioneer 
work  in  this  field  was  done  by  Van  Rysselberghe.  Fig.  22 
shows  a  modernized  arrangement  of  the  composite  system, 


TELEGRAPH  LINES  AND   CABLES  297 

and  it  will  be  observed  that  impedance  coils  and  condensers, 
for  opposing  respectively  the  alternating  telephone  and  the 
direct  telegraph  currents,  are  the  principal  features. 

It  is  seen  that  the  upper  and  lower  telegraph  currents 
are  confined  to  their  respective  line  wires  because  of  the 
condensers  c\.  The  condensers  &i  eliminate  sparking  at 
the  key  contacts  and  also  take  care  of  the  rise  and  fall 
of  the  current  in  the  telegraph  circuit  so  as  not  to  influence 
the  telephone  instruments.  The  telephone  circuit  includes 
both  line  wires  and  the  four  condensers  c\.  Because  of  the 
high  impedance  of  the  retardation  coils  Z  to  alternating 
currents  of  high  frequency  (telephone  currents  are  often 
considered  to  have  a  representative  frequency  of  800  cycles 
per  second),  the  telephone  cur- 
rents are  prevented  from  enter- 
ing the  telegraph  circuits.  The 
function  of  the  retardation  coils 
R  and  condensers  c  is  to  balance 
the  telephone  line  and  guard 
against  mutual  interferences  be- 
tween the  telephone  and  tele- 
graph circuits.  The  two  coils 

Fig.  23. 

R  at   each   end  may    also    be 

replaced   by    a   repeating    coil    of    the    type    shown    in 

Fig.  21. 

The  following  numbers  indicate  the  order  of  magnitude 
of  the  condenser  capacities:  c  =  2  mf.,  c\  =  2  mf.  and 
c2  =  6  mf .  The  impedances  Z  and  R  are  windings  on  soft 
iron  cores  of  the  closed  type  (Fig.  23)  and  possess  large 
inductance;  their  resistances  are  respectively  50  and  30 
ohms. 

Telephone  ringing  over  composited  lines  by  the  usual 


298 


TELEGRAPH   ENGINEERING 


low-frequency  generators  (about  16  cycles)  is  unsatisfactory 
because  the  impedance  of  the  retardation  coils  Z  is  small 
to  these  ringing  currents,  resulting  in  chattering  of  the 
relay  armatures.  Instead,  calling  is  accomplished  by 
means  of  weak  high-frequency  currents  (about  300  cycles) 
over  the  lines  which  actuate  suitable  relays  that  control 
the  operation  of  local  low-frequency  ringing  devices. 

Phantom  Circuits  with  Simplexed  and  Composited  Tele- 
phone Lines.  —  Two  telephone  circuits,  each  adapted  for 
simplex  telegraphic  signalling,  as  shown  in  Fig.  21,  may 
also  simultaneously  serve  as  the  conductors  of  a  phantom 


Fig.  24. 

telephone  circuit,  as  shown  schematically  in  Fig.  24.  The 
location  of  the  simplex  telegraphic  apparatus  is  indicated 
by  the  letters  A,  B,  C  and  D.  In  a  similar  manner,  two 
telephone  circuits,  each  adapted  for  composite  working  as 
shown  in  Fig.  22,  may  also  simultaneously  serve  as  the 
conductors  of  a  phantom  telephone  circuit,  thereby  secur- 
ing 4  telegraphic  and  3  telephonic  channels  over  4  wires. 

Railway  Composite  Signalling.  —  Telephonic  and  tele- 
graphic communication  may  also  be  effected  simultaneously 
over  a  single  line,  both  services  utilizing  the  ground  as  the 
return  path.  Such  telephonic  transmission  over  existing 


TELEGRAPH  LINES  AND   CABLES 


299 


telegraph  lines  is  possible  over  distances  up  to  say  200 
miles,  and  is  therefore  useful  principally  in  supplementing 
telegraphic  signalling  on  railway  telegraph  lines. 

The  arrangement  of  the  apparatus  at  a  terminal  station 

for  such  composite  signalling  differs  from  that  used  with 

magneto  or  common-battery   systems,   and  is   shown  in 

Fig.  25.     Several  intermediate  telegraph  and  intermediate 

z 


Fig.  25. 


telephone  sets  may  be  operated  on  a  line,  code  signalling 
being  utilized  for  telephonic  calling.  Portable  telephone 
sets  may  be  carried  on  the  trains  so  that  in  cases  of  emer- 
gency one  may  be  bridged  from  the  line  to  ground  at  any 
place,  enabling  prompt  requests  for  directions  or  assist- 
ance. At  intermediate  telegraph  stations  a  condenser  and 
a  resistance  bridge  the  telegraph  set  so  as  to  maintain  the 
continuity  of  the  line  for  telephonic  currents,  and  to  pre- 
vent the  high-frequency  signalling  current  affecting  the 
telegraph  relay. 

Referring  to  Fig.  25,  the  presence  of  the  impedance 
coil  Z  prevents  telephone  currents  passing  through  the  re- 
lay, as  before ;  also  the  presence  of  the  condenser  C  hinders 
the  telegraph  currents  from  entering  the  telephone  circuit. 
The  signalling  current  is  produced  by  an  induction  coil  / 


300  TELEGRAPH  ENGINEERING 

with  a  vibrator,  the  coil  also  serving  for  transmission  pur- 
poses when  talking.  The  signal-receiving  device  is  a 
special  telephone  receiver  or  howler  h,  with  a  heavy  dia- 
phragm, which  is  responsive  to  incoming  high-frequency 
signalling  currents. 

To  signal  another  telephone  station  the  keys  K\  and  KI 
are  depressed;  in  reality  both  keys  are  combined  so  they 
will  open  and  close  together.  The  closing  of  key  K\  sets 
the  armature  of  induction  coil  /  in  vibration,  and  the  core 
is  repeatedly  magnetized  and  demagnetized.  The  alter- 
nating current  induced  in  the  other  winding  thereby  flows 
from  ground,  through  the  lower  contacts  of  hook-switch 
H  and  key  K2,  through  coil  /  and  condenser  C  to  the  line. 
At  the  other  stations  this  signalling  current  flows  through 
the  condenser  C,  howler  h,  upper  contact  of  key  K2  and 
lower  contact  of  hook-switch  H  to  ground,  thus  operating 
the  howler. 

Having  secured  the  distant  station  attendant,  the  keys 
are  released  and  the  receiver  R  is  lifted  from  the  hook. 
The  local  transmitter  circuit  is  now  completed  and  the 
receiver  is  placed  in  connection  with  the  line  through  the 
condenser  C  and  the  secondary  winding  of  the  induction 
coil. 

PROBLEMS 

1.  For  a  factor  of  safety  of  5  against  wind  pressure,  what  should 
be  the  diameter  of  poles  at  the  ground  line  for  supporting  10  No.  6 
B.  W.  G.  iron  wires  at  intervals  of  100  feet  along  a  straight  path? 
The  poles  project  25  feet  above  the  ground  and  the  center  of  load 
may  be  considered  as  5  feet  from  the  pole-tops.     Allow  8000  pounds 
per  square  inch  as  the  breaking  fibre  stress  of  the  poles,  and  assume 
an  ice  coating  \  inch  thick  all  around  the  conductors. 

2.  What  sag  should  be  allowed  in  zoo-foot  spans  of  No.  9  B.  &  S. 
gage  hard-drawn  copper  wires  while  being  strung  at  a  temperature 


TELEGRAPH  LINES  AND   CABLES 


3OI 


of  80  degrees  fahr.,  so  that  the  tension  in  the  wires  with  a  £-inch  ice 
coating  at  —  20  degrees  fahr.  will  not  exceed  300  pounds  ? 

3.  Determine  the  economic  pole  spacing  for  a  pole  line  with 
No.  12  B.  &  S.  gage  hard-drawn  copper  wires  in  which  the  maximum 
allowable  tension  is  specified  as  100  pounds.     The  wires  are  to  have 
a  minimum  clearance  of  20  feet  above  ground,  the  cost  of  cross- 
arms,  insulators,  pins,  etc.,  is  $2.00  per  pole,  and  the  pole  cost- 
constant  is  a  =  0.005. 

4.  Estimate  the  cost  per  mile  installed  of  two  zoo-conductor  (No. 
14  B.  &  S.)  lead-covered  telegraph  cables  located  in  a  clay  under- 
ground conduit,  with  manholes  440  feet  apart,  each  costing  $75.00. 
The  cost  of  drawing  the  cables  in  the  conduit  and  splicing  the  con- 
ductors may  be  assumed  as  7  cents  per  foot  of  cable. 

5.  Millivoltmeter  readings  over  6-foot  lengths  of  a  lead-sheathed 
cable,  taken  at  two  successive  manholes,  were  i.o  and  0.25  milli- 
volts.   If  the  outside  diameter  of  the  sheath  is  2.5  inches  and  the 
thickness  of  its  wall  is  £  inch,  determine  the  current  leaving  the 
cable-sheath  to  ground  between  the  manholes,  the  resistivity  of  lead 
being  taken  as  8  microhms  per  inch  cube. 

6.  Two  auxiliary  grounds  were  employed  in  the  measurement  of 
the  ground  resistance  at  a  newly-constructed  permanent  ground, 
and  a  battery  in  series  with  an  adjustable  resistance  of  r  ohms  was 
successively  bridged  from  one  ground  electrode  to  each  of  the. others. 
The  voltage  V  across  the  battery,  the  voltage  drop  V  over  the  re- 
sistance r  and  the  earth  potential  difference  E  volts  were  observed 
for  each  case  with  a  voltmeter,  resulting  in  the  following  data: 


Quantity 

From  perma- 
nent to  first 
auxiliary 
ground 

From  perma- 
nent to  second 
auxiliary 
ground 

Across  the  two 
auxiliary 
grounds 

r 

70 

50 

110 

V 

10.3 

IO.O 

II.  0 

V 

6.8 

7.2 

7.8 

E 

0-3 

-O.I 

O.  2 

The  ground  resistance  of  each  path  is 


V  -  V  +  E 
V 


r,  whence  the 


resistance  of  the  permanent  ground  may  be  computed. 


302  TELEGRAPH  ENGINEERING 

7.  Two  No.  9  B.  &  S.  gage  copper  wires  one  foot  apart  hori- 
zontally are  suspended  25  feet  above  the  ground.     Calculate  the 
total  inductance  per  mile  of  both  wires  for  currents  in  the  same  and 
in  opposite  directions. 

8.  A  single  conductor  0.30  inch  in  diameter  is  surrounded  by  two 
concentric  layers  of  insulating  material  each  0.25  inch  thick,  the 
inner  and  outer  layers  having  specific  capacities  of  3  and  2  respec- 
tively, and  these  are  surrounded  by  a  metallic  armor.     Compute  the 
capacity  of  this  cable  per' mile  of  length. 

9.  Draw  a  scheme  of  connections  for  compositing  two  telephone 
circuits  which  serve  simultaneously  as  the  physical  circuits  of  a 
phantom  telephone  circuit. 


CHAPTER  X 

THEORY  OF  CURRENT  PROPAGATION  IN  LINE 
CONDUCTORS 

i.  The  Transmission  of  Current  Impulses  along  Tele- 
graph Lines.  —  The  currents  at  any  instant  that  pass 
different  points  of  a  line  conductor  differ  from  each  other, 
and  become  less  and  less  the  more  remote  the  point  of 
consideration  is  from  the  generator  end  of  the  line  con- 
ductor. This  is  due  to  the  distributed  nature  of  the  four 
line  constants:  resistance,  inductance,  capacity  and  leak- 
ance.  In  determining  the  effect  at  any  place  on  a  telegraph 


Fig.  i. 

line  of  impressing  an  electromotive  force  at  one  or  both 
of  its  terminals,  it  is  necessary  to  consider  the  conditions 
existing  in  telegraphic  transmission.  The  nature  of  the 
impulses  to  be  transmitted  by  a  telegraph  line  may  be 
inferred  from  graph  (a),  Fig.  i,  which  indicates  the  sequence 
and  duration  of  the  voltage  applications  to  the  line  for 
the  -word  "thumb."  It  is  seen  from  this  figure  that 
telegraphic  transmission  involves  the  propagation  of  long 

303 


304  TELEGRAPH   ENGINEERING 

and  short  unidirectional  impulses  of  constant  magnitude 
hj  which  are  variously  grouped  and  spaced.  The  theory 
of  propagation  of  such  irregular  impulses  may  be  con- 
sidered in  the  following  ways: 

a.   The  impulses  may  be  considered  as  made  up  of  a 

continuously  applied  direct  current  of  magnitude  -,  upon 
which  is  superposed  an  alternating  current  of  rectangular 
wave-shape  of  amplitude  - .  While  this  rectangular  wave- 

2 

shape  is  susceptible  to  resolution  into  a  Fourier's  Series  of 
sine  curves  whose  relative  frequencies  are  the  successive 
odd  numbers,  it  is  much  more  convenient  in  the  theory 
of  telegraphic  transmission  to  consider  a  single  equivalent 
sine-wave  alternating  current  rather  than  such  a  multiplicity 
of  harmonics  which  together  constitute  the  actual  impulse. 
Graphs  (b)  and  (c),  Fig.  i,  reveal  the  approximation  of 
" equivalent"  sine  curves  to  dot  and  dash  wave-shapes 
respectively,  the  amplitude  being  conveniently  taken  as 

2 

-  h.    The  frequencies  of  the  equivalent  alternating  cur- 

o 

rents  in  the  two  cases  correspond  respectively  to  the  number 

of  dots  and  to  the  number  of  T's  which  may  be  sent  out  on 
the  line  per  second,  the  latter  frequency  being  ^  of  the 
former  or  dot-frequency.  Neither  frequency  prevails  for 
more  than  several  cycles,  but  nevertheless  this  alternating- 
current  theory  of  transmission  leads  to  an  approximate  idea 
of  the  propagation  of  telegraphic  characters,  especially 
when  the  speed  of  signalling  approaches  the  theoretically 
attainable  limit  imposed  by  the  conductor.  It  may  be  re- 
marked that  a  somewhat  similar  condition  exists  in  teleph- 
ony, for  in  practical  telephonic  transmission  calculations  a 


CURRENT  PROPAGATION   IN   LINE   CONDUCTORS     305 

"representative  "  frequency  of  800  cycles  per  second  is 
considered  appropriate  for  a  single  equivalent  sine-wave 
alternating  current,  which  is  recognized  in  preference  to 
a  constantly-varying  series  of  complex  wave-shapes  that 
actually  constitute  articulate  speech.  The  frequency  of 
the  equivalent  telegraphic  alternating  current  to  be  used  in 
any  particular  calculation  depends  upon  the  speed  of  sig- 
nalling, the  dot-frequency  varying  possibly  from  15  cycles 
or  less  with  hand  transmission  to  125  cycles  with  automatic 
transmission.  The  computed  sinusoidal  current  wave-shape 
at  any  point  of  the  line  may  then  be  reduced  to  its  corre- 
sponding rectangular  wave-shape. 

0.  If  the  speed  of  telegraphic  signalling  over  a  line  is 
much  below  that  theoretically  attainable  thereon,  the  time 
of  growth  and  fall  of  the  unidirectional  current  impulse 
will  be  short  in  comparison  to  the  duration  of  a  dot  signal, 
and  consequently  the  steady  value  of  the  current  at  every 
place  on  the  line  will  be  reached  within  every  signal.  There- 
fore the  magnitude  of  the  received  impulses  may  be  ascer- 
tained on  the  basis  of  a  maintained  direct  current  flowing 
over  the  line,  the  effects  of  inductance  and  capacity  being 
ignored  because  these  constants  influence  only  the  growth 
and  fall  of  the  current  value.  This  method  of  treatment 
may  be  termed  the  direct-current  theory  of  transmission. 

7.  On  the  contrary,  if  the  speed  of  signalling  is  such  that 
the  current  at  any  place  does  not  nearly  assume  the  ulti- 
mate value  that  accompanies  slower  signalling  during  the 
time  of  dot  or  dash  signals,  then  a  consideration  of  the 
growth  and  subsequent  fall  of  the  current  alone  is  of  im- 
portance. This  consideration  of  occurrences  during  the 
repeated  transitional  periods  of  application  and  with- 
drawal of  voltage  on  the  line  may  be  called  the  transition 


306  TELEGRAPH   ENGINEERING 

theory  of  transmission,  and  is  utilized  chiefly  in  the  treat- 
ment of  submarine  cable  telegraphy  for  computing  the 
shape  of  arrival  current  curves. 

The  transmission  theories  just  enumerated  will  be  con- 
sidered in  the  order  named,  the  first  two  being  developed 
in  the  present  chapter  while  the  third  is  discussed  in  the 
following  chapter  devoted  to  submarine  telegraphy. 

Alternating-current  Transmission  Theory 

2.  Propagation  of  Alternating  Currents  along  Uniform 
Conductors  of  Infinite  Length.  —  The  impression  of  a 
sinusoidal  or  harmonic  alternating  E.M.F.  upon  a  localized 
circuit,  having  resistance  R,  inductance  L  and  capacity  C, 
initiates  three  reactions  of  the  circuit  as  follows:  (a)  re- 
sistance reaction  (RIf),  the  overcoming  of  which  produces 

heat;    (b)  inductance  reaction  (I,—-),  the  overcoming  of 

\     at  J 

which  develops  a  magnetic  field;  (c)  capacity  reaction 
[  —  /  I'dt\  the  overcoming  of  which  forms  an  electrostatic 

field;  where  I'  is  the  instantaneous  current  value,  and  / 
represents  time.  With  long  line  circuits  the  electrical 
constants  of  the  circuit  are  distributed  in  space,  and  con- 
sequently the  current,  while  everywhere  sinusoidal,  has  not 
the  same  value  or  phase  throughout  the  circuit. 

The  simplest  case  of  alternating-current  wave  propa- 
gation is  that  on  conductors  of  infinite  length,  since  on 
such  lines  the  effect  of  reflection  of  the  waves  at  the  distant 
end  can  be  ignored.  Consider  the  element  ds  of  an  infinitely 
long  uniform  line  with  a  perfectly-conducting  ground  re- 
turn, at  a  distance  s  from  the  end  upon  which  a  simple 
harmonic  electromotive  force  is  impressed,  as  shown  in 


CURRENT  PROPAGATION   IN   LINE    CONDUCTORS     307 

Fig.  2.  A  current  will  flow  through  the  conductor,  and  at 
the  instant  t  at  the  element  ds  it  may  be  represented  by 
/',  and  that  in  the  adjacent  elements  by  I'  +  dl'  and 
/'  —  dl1 ',  the  latter  referring  to  the  element  more  remote 
from  the  generator.  Let  E',  at  this  instant,  be  the  poten- 
tial of  the  line  with  respect  to  the  earth  at  the  element  ds 
and  let  the  potentials  of  the  adjacent  elements  above  that 
of  the  earth  be  E'  +  dEf  and  E'  -  dE'  respectively.  Let 
R,  L  and  C  in  homologous  units  represent  respectively  the 

i  i'  i  i-ai' 


Ground 


Fig.  2. 

uniformly  distributed  resistance,  inductance  and  capacity 
of  the  line  per  unit  length. 

The  difference  of  potential  between  the  two  ends  of  the 
element  ds  is  dE'  and  this  must  be  equal  to  the  sum  of  the 
resistance  and  inductance  reactions  of  the  elementary  cir- 
cuit occasioned  by  the  current  /'.  As  only  the  reactions 
of  the  conductor  need  be  considered,  there  results  for  this 
element 


*f+—  -f-  •,-.    <-> 

Since  the  line  has  capacity  with  respect  to  earth,  it  takes 
a   charging  current;    and  since  the  line  is  not  perfectly 


308  TELEGRAPH   ENGINEERING 

insulated  from  ground,  a  slight  leakage  current  will  flow. 
Therefore  the  current  which  does  not  continue  beyond  the 
element  ds,  but  which  flows  from  the  line  to  ground  under 
the  voltage  E',  is 


where  g,  the  leakage  conductance  or  leakance,  is  the  recipro- 
cal of  the  apparent  insulation  resistance  per  unit  length  of 
line.  Then 

_<^-Cd-^  +  E'z  (2) 

ds~     '   dt       *g' 

Differentiating  (i)  with  respect  to  time,  there  results 


^  dt*  dt          dt\ds 

and  differentiating  (2)  with  respect  to  distance,  there  results 

Substitution  of  the  former  in  the  latter  equation  gives 

dl'        dE' 


and  replacing  the  last  term  by  its  equivalent  from  (i)  there 
is  obtained  the  equation  of  propagation  of  current  along  a 
uniform  line,  as 


the  solution  of  which  shows  the  current  value  at  the  point  s 
of  the  line  at  the  time  t  in  terms  of  the  line  constants 
R,  L,  C  and  g. 


CURRENT  PROPAGATION  IN  LINE    CONDUCTORS     309 

Similarly,  by  differentiating  (i)  with  respect  to  distance, 
and  (2)  with  respect  to  time,  and  then  combining  the  re- 
sulting expressions,  there  is  obtained 

dE'      d2E' 


Equations  (3)  and  (4),  for  current  and  voltage  distribution 
respectively,  are  true  for  any  length  of  line,  and  are  identi- 
cal, so  that  the  solution  of  one  of  them  suffices. 

Since  the  magnitude  of  the  current  must  decrease  in  re- 
ceding from  the  generator  end  of  the  infinitely  long  line, 
and  since  the  current  is  simple  harmonic  when  the  impressed 
electromotive  force  is  such,  and  differs  in  phase  therefrom 
more  and  more  as  s  increases,  the  following  representation 
of  the  current  at  any  point  s  of  the  infinitely  long  line  at  the 
time  /  suggests  itself: 

/'=/€-*  cos  (#-  as),  (5) 

where  7  is  the  maximum  value  of  the  current  at  the  genera- 
tor end  of  the  line,  p  is  2  T  times  the  frequency  of  the  im- 
pressed harmonic  electromotive  force,  e~^  is  the  diminution 
in  magnitude  of  the  wave  over  unit  length  of  circuit,  a  is  the 
phase  retardation  per  unit  distance  which  in  degrees  is 

—  ,  j8  and  a  being  constants  which  depend  upon   the 

resistance,  inductance,  capacity  and  leakance  of  the  line, 
and  c  being  the  base  of  Napierian  logarithms. 

The  substitution  of  this  assumed  expression  for  the  cur- 
rent I'  with  proper  values  of  a  and  /3  in  (3)  will  satisfy  this 
equation  and  permit  of  the  evaluation  of  the  constants  a 
and  /3.  Thus,  differentiating  (5)  with  respect  to  time, 

'  =  -  pi€-»  Sin  (Pt  -  «s), 


310  TELEGRAPH  ENGINEERING 

and  again, 

rPJ' 

£-  --#*/«-*  COS  (#-  as)  j 


and  differentiating  with  respect  to  distance, 
sin  (pt  -  as)  -  ftle^*  cos  (pt 
a  sin  (pt  -as)  -ft  COS  (pt  -as)}, 


JTf 

—  =  air*8  sin  (pt  -  as)  -  ftle^*  cos  (pt  -  as) 


and  again, 

J2Tt 

—  =  /€Hfc{  -  a*  cos  (pt  -  as)  -  aft  sin  (pt  -  as)  } 
-  Pie'?8  {  a  sin  (pt  -  as)  -  ft  COS  (pt  -  as)  } 
=  7e-^[(/32  -  a:2)  COS  (pt  -  as)  -  2  aft  sin  (pt  -  as)]. 

Substituting  these  values  in  equation  (3),  there  results, 

^cos  (pt  -  as)  -  (RC  +  gL)  pie-**3  sin  (pt  -  as) 
*  COS  (pt  -  as)  -  le-P*  [(ft2  -  a2)  COS  (pt  -  as) 
—  2  aft  sin  (pt  —  as)]  =  O, 
or 

p2CL  cos  (pt  -  as)  +  p  (RC  +  gL)  sin  (pt  -  as) 
-  Rg  COS  (pt  -  as)  +  (ft2  -  a2)  COS  (pt  -  as) 
—  2  aft  sin  (pt  —  as)  =  O. 

This  expression  can  only  be  true  if 

fCL  -Rg  =  -(0*-  «2)  =  c?  -  p,  (6) 

and  if 

p  (RC  +  gL)=2  aft.  (7) 

These  are  simultaneous  equations  which  can  be  solved  for 
a  and  ft.  Thus,  substituting  the  value  of  a  from  (7)  in  (6) 
gives  the  following  biquadratic: 

=  o, 


CURRENT  PROPAGATION  IN  LINE   CONDUCTORS     311 
whence 


(RC- 

p*L2C2-p2LC  +  Rg]. 
Therefore, 

(8) 


and  similarly 

(9) 


The  constant  /3  is  called  the  attenuation  coefficient,  and  a 
is  called  the  wave-length  constant.  Having  determined  the 
values  of  a  and  0,  the  current  at  any  point  on  the  line  dis- 
tant s  from  the  generator  at  the  time  t  may  be  determined 
when  the  maximum  current  value  is  known  at  the  end  upon 

which  the  electromotive  force  of  frequency  -2-  is  impressed. 

At  some  other  point  on  the  line  distant  r  from  the  genera- 
tor end,  the  current  value  at  the  instant  /  is 

//  =  /€-*  cos  (pt  -  or). 

If  this  more  distant  point  r  be  chosen  so  that  the  current 
there  will  be  in  phase  with  that  at  the  point  s  at  that  in- 
stant, then 

cos  (pt  —  as)  =  cos  (pt  —  or). 

Between  these  points  r  and  s  there  is  an  integral  number  of 
complete  waves,  n;  therefore,  the  wave-length  is 


n 


Since  the  phase  retardation  can  be  considered  over  this 
distance  as  2  irn, 

as  +  2  irn  =  ar: 


312  TELEGRAPH    ENGINEERING 

consequently, 


r  —  s  _ 


a          n 

As  the  frequency  of  the  impressed  electromotive  force  is 
—  cycles  per  second,  the  velocity  of  wave  propagation 
will  be 

v  =  -£-\  =  £>  (10) 

27T          a 

In  cables,  because  of  the  close  proximity  of  the  conduc- 
tors to  one  another,  the  inductance  is  little  and  the  capacity 
large.  Since  2  irf  times  the  inductance  is  small  compared 
with  the  resistance  of  the  conductors,  and,  in  good  telegraph 
and  telephone  cables,  as  the  conductance  of  the  insulation  is 
small  compared  with  2  irf  times  the  capacity,  the  attenua- 
tion constant  of  such  cables  may  be  expressed  in  a  more 
convenient  form  by  expanding  the  factors  \^R2  +  P2L2  and 
^/p2C2  +  g2  of  equation  (8)  by  the  binomial  theorem  and 
disregarding  terms  of  higher  order  than  the  second  as  being 
too  small  to  make  any  appreciable  difference.  Then 


*(>+m^(>+^] 

PCR(*  -i-^-i — £—  4— f?£-\ 


Neglecting  the  last  term  for  similar  reasons,  the  attenuation 
constant  becomes 


CURRENT  PROPAGATION  IN  LINE   CONDUCTORS     313 
If  the  inductance  be  entirely  ignored,  there  results  herefrom 


by  disregarding      g  2     •      This  expression  is  convenient  in 

considering  wave  transmission  over  cables.     If  the  leakage 
conductance  be  taken  as  zero,  it  reduces  to 


3.   Velocity  of  Wave  Propagation  over  an  Ideal  Line.  - 

An  ideal  line  may  be  considered  a  perfectly  insulated  one 
employing  conductors  of  zero  resistance,  for  then  the  at- 
tenuation would  be  nil.  Thus,  by  substituting  in  (8)  and 
(Q)>  g  =  °  and  R  =  o,  there  results 

0  =  o    and    a  =  p  VZC. 
Therefore,  the  velocity  of  wave  propagation  on  such  a  line 

would  be  v  =  -    —-  (n) 

VLC 

The  inductance  of  a  straight  conductor  due  to  the  mag- 
netic flux  surrounding  the  conductor,  in  electromagnetic 
units  per  centimeter  length,  is 

d-D 


and  the  capacity  thereof  in  electrostatic  units  per  centi- 
meter length  is  ^ 

d-D* 


where  D  is  the  diameter  of  the  wires  and  d  is  their  inter- 
axial  separation. 


314          TELEGRAPH  ENGINEERING 

As  there  are  9  X  lo20  electrostatic  units  in  one  electro- 
magnetic unit  of  capacity,  the  square  root  of  the  product  of 
these  expressions  in  electromagnetic  units  is 


3  X  io10 

Therefore,  the  velocity  of  electric  wave  propagation,  when 
the  resistance  and  leakance  of  the  conductors  are  neglected,  is 

3  X  io10 
v  =  ^     —  —  centimeters  per  second.  (12) 


With  conductors  in  a  medium  like  air,  for  which  both  the 
permeability  /*  and  the  permittivity  k  are  unity,  the  velocity 
of  propagation  is  300,000  kilometers  per  second  (186,000 
miles  per  second),  which  is  identical  with  the  velocity  of 
light.  For  actual  lines  the  velocity  of  wave  propagation 
is  somewhat  lower  than  this  value. 

4.  Wave  Propagation  along  Conductors  of  Finite  Length. 

—  In  the  foregoing  discussion  of  wave  propagation  on  in- 
finitely long  lines,  no  cognizance  was  taken  of  reflection 
of  the  outgoing  waves  upon  arrival  at  the  distant  terminal 
of  the  circuit.  Voltage  and  current  waves,  which  together 
constitute  an  electromagnetic  wave,  when  traversing  rela- 
tively short  circuits  having  distributed  capacity  and  induc- 
tance, are  partially  reflected  at  both  ends  thereof  with  or 
without  phase  reversal,  total  reflection  taking  place  only 
when  the  impedances  at  the  terminals  of  the  lines  are  either 
zero  or  infinity  (that  is,  short-circuited  or  open-circuited). 
If  a  single  impulse  be  impressed  upon  the  circuit,  a  wave  will 
travel  back  and  forth  along  the  line,  until  it  is  attenuated 
to  practically  nothing.  If  such  waves  continually  depart 


CURRENT  PROPAGATION  IN  LINE   CONDUCTORS     315 

from  one  end  of  a  line,  and  each  wave  is  reflected  a  great 
many  times,  alternately  at  the  other  and  initial  ends  of  the 
circuit,  before  extinction,  the  current  and  voltage  every- 
where on  the  line  will  be  gradually  built  up  and  ultimately 
assume  their  final  values.  This  steady  state  is  approached 
by  successive  jumps  and  not  uniformly,  although  attained 
in  a  very  short  time  —  perhaps  a  second.  After  the  steady 
state  is  reached,  all  the  outgoing  waves  may  be  considered 
together  as  a  single  resultant  wave-train,  and  all  the  re- 
turning waves  as  another  single  wave-train.  The  following 
method  of  deriving  the  equations  of  current  and  voltage 
distribution  on  lines  of  finite  length  for  the  steady  state 
displays  the  results  physically  as  two  oppositely  moving 
wave-trains,  each  of  definite  initial  amplitude.  By  not  con- 
sidering the  short,  unsteady  period  immediately  following 
the  voltage  application,  a  simplification  of  operations  may 
be  effected  over  the  foregoing  method  of  treatment  by  intro- 
ducing the  complex  quantity,  inasmuch  as  one  independent 
variable  —  that  of  time  —  is  eliminated  thereby.  The 
resulting  expressions  are  complex  quantities  and  their  in- 
terpretation must  be  made  accordingly. 

Harmonically  varying  quantities  can  be  represented  by 
vectors.  The  length  of  such  a  vector  shows  the  maximum 
value  of  the  quantity,  and  its  direction  indicates  the  phase 
of  that  quantity.  Each  vector  may  be  resolved  into  two 
rectangular  component  vectors,  say,  one  horizontal  and  the 
other  vertical.  To  distinguish  vertical  from  horizontal 
components,  a  symbol,  usually^',  is  placed  before  the  verti- 
cal component.  Thus,  the  expression  a  +  jb  means  that  b 
is  to  be  added  vectorially  at  right  angles  to  a.  Obviously 
the  magnitude  of  the  resultant  vector  is  Va2  -{-  b2,  and 
the  angle  it  makes  with  the  horizontal  component  is 


316  TELEGRAPH  ENGINEERING 

tan"1  -  •    The  interpretation  of  this  quadrantal  operator  or 
a 

neomony  isj  =  V—  i. 

By  applying  the  operator  to  equations  (i)  and  (2)  and 
counting  the  distance  s  positive  from  the  receiving  end  of 
the  line,  it  follows  that  for  the  steady  state 


(13) 
and 

(14) 


which  are  relations  independent  of  time,  wherein  Em  and 
Im  represent  the  maximum  values  of  electromotive  force 
and  current  respectively  at  any  point  on  the  circuit.  The 
factor  (R  -\-jpV)  may  be  called  the  conductor  impedance, 
and  (g  -\-jpC)  the  dielectric  admittance.  Differentiating 
these  expressions  and  substituting  gives  respectively 


and 

^=(R+jpL)(g+jpC)Im. 

For  convenience,  let  (R  +  jpL)(g  +  jpC)  =  y2,  then  the 
equations  of  wave  propagation  along  conductors  become 

;,    .,'  f-^  '      ;<« 

and 

^df  =  y2Im'  (l6) 

These  are  identical  differential  equations  of  electromotive 
force  and  current  which  differ  in  the  terminal  conditions 


CURRENT  PROPAGATION   IN   LINE   CONDUCTORS     317 

only,  and  consequently  the  solution  of  one  of  them  will 
suffice. 

Choosing  the  latter  expression  and  multiplying  through 

by  2  —  -  j  there  results 

d*Im    dln  dlm 

2  ~7~z  ---  T~  =  2  rlm  ~T~' 
ds2      ds  ds 

which,  when  integrated,  becomes 


Replacing  the  constant  of  integration  c\  by  72c22,  where  c^  is 
also  a  constant,  and  separating  the  variables,  there  obtains 

dlm 


=  yds. 


V/ro2 

Integration  gives 

loge  [C3(lm  + 

where  c3  is  another  constant  of  integration.     Writing  in 
exponential  form,  this  equation  becomes 


Squaring, 


or  -T-c22  =  2/ro  —  J 

C32  C3 

whence 

/     _  *"  _  tfc* 

2C3         26^' 

Choosing  constants  A  and  B  so  that 

A  =  —   and  B  =  ^ 


318  TELEGRAPH    ENGINEERING 

the  expression  for  the  maximum  value  of  the  current  at  a 
distance  s  from  the  receiving  end  of  the  line  becomes 

Im  =  Ae^8-  B*"»,  (17) 

where  the  two  constants  must  be  evaluated  from  the  termi- 
nal conditions. 

Since  the  exponential  coefficient  7  is  the  square  root  of 
the  product  of  two  complex  numbers,  it  is  also  a  complex 
quantity,  and  may  be  written 

7  =  0  +ja, 
where  a  and  0  are  its  two  rectangular  components.     Then 

08  +ja)»  =  (R  +jpL)(g  +jfQ,  (18) 

or 

02  +  2ja0  +JW  =  Rg  +jgpL  +jpRC  + 

and  remembering  that  j  =  V—  i,  this  becomes 
(02  -  a2)  +  2ja0  =  (Rg  -  P2CL)  +j  (gpL  + 
This  equation  can  only  be  true  if 

c?-f?  =  fCL  -  Rg, 
and  if 

2a(3  =  p(RC  +  gL). 

These  expressions  are  identical  with  equations  (6)  and  (7), 
and,  therefore,  the  components  of  7  have  the  same  signifi- 
cance as  before;  namely,  0  is  the  attenuation  coefficient  and 
a  is  the  wave-length  constant,  the  values  of  which  are  given 
by  equations  (8)  and  (9)  respectively.  The  quantity  7  is 
called  the  propagation  constant  of  the  line. 

The  maximum  current  value  at  a  point  on  the  line  distant 
s  from  the  receiving  end  may  now  be  indicated  as 


Writing  for  the  exponential  function  with  the  imaginary 
exponent  the  equivalent  trigonometric  expression  e±:>as  = 


CURRENT  PROPAGATION  IN  LINE  CONDUCTORS     319 

cos  as  ±7  sin  as,  the  equation  for  Im  becomes 

Im  =  A<?8  (cos  as  +j  sin  as)  —  Bt~v*  (cos  as  —j  sin  as),    (19) 

the  first  term  of  which,  since  it  increases  as  5  increases,  may 
be  considered  the  main  current  wave,  and  the  second  term 
may  be  called  the  reflected  current  wave.  The  amplitudes 
of  these  waves  at  the  receiving  end  are  respectively  A  and  B. 
The  maximum  value  of  the  voltage  at  the  same  point  on 
the  line  can  be  obtained  by  differentiating  (19)  or  (17)  and 
substituting  in  equation  (14), 

Em  =      ,    /"  [A  f9  (cos  as  +  j  sin  as) 

g+jpc 

+  Be~08  (cos  as  —  j  sin  as)].  (20) 

To  evaluate  the  constants  A  and  B,  two  conditions  must 
be  known,  as  current  and  voltage  at  one  end  of  the  line,  or 
current  at  one  terminal  and  voltage  at  the  other  terminal 
of  the  line;  thus,  at  the  receiving  end  s  =  o,  and  equations 
(19)  and  (20)  give  the  maximum  current  and  voltage  values 
respectively  at  this  point  as 

Ir  =  A-B, 

and 


The  fraction  &  +ja  +  g  +jpC  is  frequently  called  the 
surge  impedance  or  characteristic  impedance  of  the  line. 
Then 


and 

'       (22) 


The  ratio  of  the  amplitude  of  the  reflected  wave  to  that 
of  the  main  wave  arriving  at  the  receiving  end,  that  is,  the 


320 


TELEGRAPH    ENGINEERING 


ratio  of  B  to  A  ,  will  depend  upon  the  character  of  the  termi- 
nal apparatus,  and  may  be  called  the  coefficient  of  reflec- 
tion. This  coefficient  is 


A  Lf  fS          |       J**. 

^R+jJi  +  " 
Representing  the  impedance  of  the  terminal  apparatus  by 
Zr,  this  expression  becomes 

Zr(p+ja)-(R+jpL)        ,x 
ZF&+ja)  +  (R+jpL) 


Zr  = 


TR+jpL 


For  total  absorption  of  the  wave,  m  =  o,  and  the  receiver 
impedance  should  be 

R  +jpL 
ft  +j<*  ' 

Substituting  the  values  of  A  and  B  in  equations  (19)  and 
(20),  the  complete  equations  for  the  maximum  values  of 
current  and  voltage  at  any  point  of  the  line  at  a  distance  s 
from  the  end  to  which  the  receiver  is  connected,  become 
respectively 


as  +j  sin  as) 


«-*  (cos  <*s  -J  sin  «*)        (*4) 


(25) 


CURRENT  PROPAGATION  IN    LINE   CONDUCTORS     321 

If  it  be  desired  to  reckon  the  distance  in  the  opposite 
direction,  that  is,  from  the  generator  to  the  receiving  ends 
of  the  line,  the  sign  of  s  must  be  reversed  in  equations  (13) 
and  (14),  and  there  result  for  the  current  and  voltage  at 
any  point  distant  s  from  the  generator  end  of  the  line, 
respectively, 


(26) 
and 


Em  =  i    E.  +  7.  ~         «-*  (cos  a*  -j  sin  as) 


where  £„  and  /„  are  the  maximum  voltage  and  current 
values  at  the  generator  end  of  the  circuit. 

The  terminal  conditions  in  any  given  problem  are  usually 
specified,  the  voltage  being  considered  the  standard  phase. 
In  the  present  notation  for  vector  rotation  a  current  lead- 
ing the  voltage  in  phase  is  written  i\  +  ji^,  and  a  lagging 
current  is  represented  by  it  —  ji^. 

The  foregoing  equations  may  also  be  employed  with 
equal  relevancy  to  calculations  involving  effective  current 
and  voltage  values  instead  of  the  maximum  values  of  these 
quantities.  Short  tables  of  exponential  and  trigonometric 
functions  appear  in  the  Appendix. 

5.   Simplified  Equations  of  Wave  Propagation.  —  The 

solution  of  the  equations  of  wave  propagation  can  be  trans- 
formed into  a  more  convenient  form,  as  shown  by  Kennelly, 


322  TELEGRAPH  ENGINEERING 

by  expanding  the  factors  e±7S  of  equation  (17).     Thus,  by 
Maclaurin's  series 


l£          [3  [4 


that  is,  e±7S  can  be  expanded  into  two  series,  one  containing 
even  powers  of  ys  and  the  other  having  odd  powers  thereof. 
From  hyperbolic  trigonometry,  these  series  are  called  re- 
spectively the  hyperbolic  cosine  and  hyperbolic  sine,  and 
are  written 


Therefore, 


i       +  •  •  -    =  cosh  7*, 

[4 

XK 

...  =sinh7, 


Equation  (17)  for  the  current  on  the  line  at  a  point  dis- 
tant s  from  the  receiving  end  may  thus  be  written 

Im  =  A  (cosh  ys  +  sinh  75)  —  B  (cosh  ys  —  sinh  75), 
or       Im  =  (A  -  B)  cosh  ys  +  (A  +  £)  sinh  7*.  (28) 

The  maximum  value  of  the  voltage  at  the  same  point 
can  be  found  by  differentiating  (28)  and  substituting  in 
equation  (14). 

Since  —cosh  ys  =  7  sinh  75, 

as 

and  —  sinh  ys  =  7  cosh  75, 

as 

there  results 

(g  +JPC)  Em  =  (A-B}y  sinh  7*  +  (A  +  B)  7  cosh  7*, 


CURRENT  PROPAGATION  IN  LINE   CONDUCTORS     323 

whence 

Em  =  ^^\(A  -  S)  sinh  7*  +  (A  +  B)  cosh  ys\   (29) 
g+jpCl  J 

The  constants  A  and  £  of  expressions  (28)  and  (29)  may  be 
determined  from  the  conditions  at  the  receiving  end  of  the 
line.  Let  Er  and  Ir  be  maximum  values  respectively  of 
the  voltage  and  the  outgoing  current  at  this  terminal. 
Then,  for  s  =  o,  since  cosh  (o)  =  i  and  sinh  (o)  =  o, 

Ir=A    -B, 

and         B' 

Substituting  these  values  yields 

Im  =  Ir  cosh  7S  +  Er  /     {"  sinh  ys,  (30) 

K  +  jpL 

and 

Em  =  Ir  ft*?a~  sinh  7*  +  Er  cosh  75.  (31) 


The  hyperbolic  functions  of  the  propagation  constant  7 
may  be  written,  since  7  =  0  +  y«, 
cosh  75  =  cosh  (0j  +y«5)  =  cosh  /3s  •  cos  as  +j  sinh  /3s  •  sin  as, 

and 

sinh  75  =  sinh  (3s  •  cos  as  -\-j  cosh  /3s  •  sin  as. 

Then  the  equations  of  current  and  voltage  at  any  point  on 
a  line  at  a  distance  5  from  the  receiving  end  thereof  are 
Im  =  Ir  (cosh  0s  •  cos  as  -\-j  sinh  0s  •  sin  as) 

+  Er  p      •?"   (sinh  185  •  cos  as  +y  cosh  /3s  •  sin  as),  (32) 
K  -rJpL 

and 

£m  =  Er  (cosh  /3s  •  cos  as  +j  sinh  /3s  •  sin  as) 

+  Ir  —     ."  (sinh  /3s  •  cos  as  +j  cosh  /3s  •  sin  as).      (33) 


324  TELEGRAPH  ENGINEERING 

When  5  is  measured  from  the  generator  toward  the  re- 
ceiving end  of  the  line,  equations  (30)  and  (31)  become 

Im  =  Ig  cosh  ys  -  Eg  R     j"  sinh  js,  (34) 

and 

Em  =  Eg  cosh  ys  -  Ig  *     ?"  sinh  7$.  (35) 


From  equation  (34)  is  seen  that  for  an  infinitely  long  line, 
on  which  the  current  at  the  inaccessible  end  is 


/.cosh  (oo)  =  £gsinh  (oo), 
whence 


0+ja  ,     . 

(36) 


By  substituting  this  value  in  the  same  expression,  the  cur- 
rent at  a  distance  s  from  the  generator  end  of  such  a  line 

becomes 

Im  =  Ig  (cosh  ys  -  sinh  ys)  =  Ig€~ys}  (37) 

which  shows  that  the  entering  current  decreases  logarith- 
mically to  zero  as  s  increases  to  oo  .  This  expression  is 
analogous  to  equation  (5).  Similarly,  on  an  infinitely 

long  line 

Em  =  Ege^s.  (38) 


Tabulated  numerical  values  of  the  hyperbolic  sines  and 
cosines  appear  in  the  Appendix.  The  hyperbolic  functions 
of  complex  quantities  may  be  obtained  directly  from  tables 
and  charts  prepared  by  Prof.  Kennelly. 

6.  Current  and  Voltage  Distribution  on  Lines  for  any 
Terminal  Condition.  —  The  current  and  voltage  relations 
in  circuits  having  distributed  capacity  and  inductance  with 


CURRENT  PROPAGATION   IN  LINE   CONDUCTORS     325 

given  terminal  conditions  under  a  given  impressed  electro- 
motive force  will  now  be  considered.  Three  cases  arise, 
namely:  a,  line  open-circuited  at  receiver;  6,  line  short- 
circuited  at  same  place;  and  c,  apparatus  of  given  impedance 
connected  to  the  receiving  end  of  the  line. 

(a)  When  the  line  is  open-circuited  at  the  receiving 
end  (IT  =  o),  the  current  Ig°,  entering  it  at  the  other  end, 
is  obtained  from  equation  (34)  by  placing  Im  =  o.  Since 

sinh  ys 


cosh  75 
there  results 


=  tanh  ys, 


where  Si  represents  the  total  length  of  the  line  conductor. 
Upon  substitution  in  equations  (34)  and  (35),  there  re- 
sults respectively  the  values  of  current  and  voltage  at 
any  point  distant  5  from  the  generator  end  of  the  line, 
when  the  other  end  is  open-circuited,  as 

7m°=  Eg  _   ,   -?°L  (cosh  ys  tanh  7*1  -  sinh  75),      (40) 
K  +JPL, 

and 

Em°  =  Eg  (cosh  ys  —  sinh  ys  tanh  751).  (41) 

When  5  =  siy  these  equations  reduce  respectively  to  the 
current  and  voltage  at  the  open  end,  viz: 

Ir°=  O,  (42) 

and  E°  --  I"—  =  E,  sech  •>*,,  (43) 

cosn  ySi 

since  cosh2  7^1  —  sinh2  7^1  =  i. 

(b)  The  current  and  voltage  relations  at  any  point  of  a 
line  which  is  short-circuited  at  the  distant  end  are  easily 


E° 


326  TELEGRAPH   ENGINEERING 

obtained,  since  the  voltage  at  that  end,  Er,  is  zero.  By 
placing  Em  =  o  when  s  =  si,  in  equation  (35),  there  results 
the  current  entering  the  circuit  as 

I       "  j*/~* 

+    a 

The  current  and  voltage  at  any  place  are,  therefore,  respec- 
tively, from  equations  (34)  and  (35), 

J 


(cosh  ys  coth  7*1  -  sinh  ys),       (45) 


Em'=  Eg  (cosh  ys  —  sinh  ys  coth  7^1).  (46) 

The  conditions  at  the  short-circuited  end  are  obtainable 
herefrom  by  replacing  s  by  si,  whence 


CSCh  7*1,        (47) 
|          a 

and  Er'  =  o. 

(c)  When  the  character  of  the  receiving  apparatus  is 
specified,  that  is,  when  its  impedance, 


is  known,  the  voltage  and  current  at  any  point  of  the  line 
may  be  determined  in  terms  of  the  impressed  electromotive 
force.  By  placing  5  =  Si,  equations  (34)  and  (35)  give  the 
current  and  voltage  at  the  receiving  apparatus;  and  divid- 
ing the  latter  by  the  former,  there  results 

E0  cosh  7*1  -  I0         ?"  sinh  7*1 


_  __  _ 

11    —  —   £j<f    ~~-   ^ 

I0  cosh  ysi  -  Ea  p      •?  "  sinh  751 
K  -\-jpL 


CURRENT  PROPAGATION  IN  LINE   CONDUCTORS      327 

from  which 

Zr  p      •?  "  sinh  ysi  +  cosh  7^ 

'•  =  E°       jp     &  +  ja  --       (48) 

Zr  cosh  ysi  +  -  —  ^  sinh  7*1 

g+jpc 

By  substituting  this  value  in  the  same  equations  there 
results  respectively  as  the  current  and  voltage  at  a  point  on 
the  line  distant  s  miles  from  the  generator: 

0+ja 
E'R+JPL* 


Zr  sinh  751  H  ---  -•*£—  cosh 


/3      i      ^ 

Zr  cosh  7*1  +      ,    r  "  sinh  7*1 

g+jpc 


•cosh  75  —  sinh  75 


,    (49) 


and  Em  =  Eg  X 

Zr  sinh  7$!  H 7—  cosh 


Q  |  " 

Zr  cosh  ysi  +  — — T^T;  sinh 


sinh  75 


•    (50) 


These  equations  may  be  more  conveniently  expressed  by 
choosing  an  angle  0  such  that 


= 

R  +jpL 

and  they  assume  the  following  forms: 

Im  =  E0  _f  "^  [coth  (T5i  +  0)  cosh  7^  -  sinh  75],    (51) 
/t  -\-jpL 

and 
£w  =  £ff  [cosh  75  —  coth  (7^1  +  0)  sinh  75].  (52) 

These  general   expressions  are  similar  in  form  to  those 
derived  under  case  (b)  . 


328  TELEGRAPH  ENGINEERING 

At  the  terminal  apparatus  of  impedance  ZP,  the  current 
and  voltage  in  terms  of  the  impressed  electromotive  force 
Eg  may  be  obtained  from  equations  (49)  and  (50)  by  putting 
$i  for  S  whence 


Zr  cosh  ysi  +      ,    . 

8+JpC 


(53) 


and 

? 

(54) 


cosh  ~ 

Zr 

The  general  expressions  (49)  to  (54)  reduce  to  those 
derived  under  cases  (a)  and  (b)  for  lines  open-  and  short- 
circuited  at  the  distant  end  by  placing  Zr  equal  to  infinity 
and  zero  respectively. 

7.  Effect  of  Impedance  at  Sending  End.  —  In  the  fore- 
going expressions  the  impedance,  Zt,  of  any  apparatus  which 
might  be  connected  to  the  generator  end  of  a  line,  such  as 
a  relay  on  a  telegraph  line,  has  been  ignored.  The  in- 
fluence of  such  impedance  can  be  taken  into  account  by 
replacing  E0  in  equations  (49)  to  (54)  by 

Ea>-  I.[R,  +j(pLt  -  ^-)]=  £/-  I,Zt,        (55) 

where  Rt,  Lt  and  Ct  are  respectively  the  resistance,  induc- 
tance and  capacity  of  the  transmitting  device,  Fig.  3,  and 
I  a  is  the  current  entering  the  line. 

This  current  value,  from  (51)  by  placing  75  =  o,  is 


CURRENT  PROPAGATION   IN  LINE   CONDUCTORS     329 
where 


which,  when  substituted  in  equation  (55),  yields 

•p  r 

£„  = 


"R+jpL 

By  replacing  the  value  of  Eg  in  equations  (51)  and  (52)  by 
this  quantity,  there  result  respectively  the  complete  and 

Im 


^////////////////^^^^^  w/////////////////^^^^^ 

Fig.  3. 

general  expressions  for  the  current  and  voltage  values  at 
any  point  on  the  line  distant  s  miles  from  the  generator 
as 

r       J7'JL+1^_    cosh  ys  •  coth  (7^1  +  </>)-  sinh  7* 

lm  =  tig     p  --   —  -  - 


and 

^    =  £  /  cosh  75  -  sinh  75  •  coth  (7*1  +  0)        /     v 

' 


By  placing  5  =  Si  in  the  foregoing  general  expressions 
for  current  and  voltage  distribution  on  lines,  the  condi- 


33°  TELEGRAPH   ENGINEERING 

tions  at  the  receiving  end  of  the  circuit  are  obtained; 
namely, 


/= 

' 


and  (58) 

T?     _    _____  Eg    Zr 

" 


(59) 

These  equations  are  together  represented  by  the  determi- 
nantal  expression 

£'  Z7 
g J^r  , ,     N 

1  -  -  -  -=-  •        (ooj 

Zr 


I  O 

i  sinh  75 1 


The  equations  derived  in  §§4-7  are  applicable  to  all 
alternating-current  circuits  having  distributed  resistance, 
inductance  and  capacity  in  the  steady  state,  and  with  any 
terminal  condition  at  either  end.  They  are  extremely  use- 
ful in  solving  transmission  problems  not  only  in  teleg- 
raphy, but  also  in  telephony  and  power  transmission.  In 
applying  the  equations  to  circuits  employing  two  or  more 
line  conductors,  the  significance  of  the  symbols  must  be 
properly  interpreted. 

8.  Illustration  of  Sine-wave  Telegraphic  Transmission. 

—  Consider  a  150- volt  (effective  value)  alternating-current 
generator  to  be  connected  to  one  end  of  a  6oo-mile  simplex 
ground-return  aerial  telegraph  line  of  No.  10  B.  &  S.  gage 


CURRENT  PROPAGATION  IN  LINE   CONDUCTORS     331 

copper  wire,  the  line  having  a  3oo-ohm  relay  at  each  termi- 
nal. Determine  the  current  and  voltage  relations  in  the 
circuit  for  a  signalling  speed  yielding  a  dot-frequency  of 
15  cycles  per  second. 

The  maximum  value  of  the  impressed  harmonic  voltage 
is  150  ^fi  or  212.2  volts,  which  may  be  considered  the 
equivalent  of  a  unidirectional  voltage  of  320  volts,  as  out- 
lined in  §  i.  The  electrical  constants  of  the  line  per  mile 
will  be  taken  as  follows: 

R  =  5.28  ohms,  (page  29) 

L  =  3.10  X  io~3  henrys,!     For  a  single  wire  25  feet 
C  =  9.54  X  io~9  farads,  J     above  ground  (page  283) 
and  g  =  2. co  X  io~6  mhos. 

While  the  inductance  of  the  relays  depends  upon  several 
conditions,  its  value  in  this  calculation  will,  however,  be 
considered  constant  at  5  henrys;  whence  the  impedance  of 
each  relay  at  15  cycles  is 

Zr  =  Zt  =  Rr  +jpLr  =  300  +  2  TT  15  X  5.7  =  300  + 
ohms,  and  the  absolute  value  is 


VRr*  +  p*L?  =  v^2  +  ^  =  558  ohms. 

The  attenuation  and  wave-length  constants  of  the  line  are 
respectively  obtained  from  equations  (8)  and  (9)  as 

j8  =  0.00331, 

and  a  =  0.000808. 

The  velocity  of  propagation  and  the  wave-length  are  re- 
spectively 


and 


1   TT    T  ^ 

V  =  88  =  II^5°  n1^68  Per  second, 


.  27T  .. 

X  = r-r  =  7770  miles. 

0.000808      ' ' ' 


332  TELEGRAPH  ENGINEERING 

Further,  since 

Si  =  600  miles, 

Ea'   =  212.2  VOltS, 

£  +JpC  =  (2-0  +  0.8997)  iQ-6  mhos, 
R  +  jpL  =  5.28  +  0.2927  ohms, 


g+jpc 


ySi  =  fa  +jaSi  =  1.986  +  0.4848^*, 
sinh  7^1  =  sinh  1.986  •  cos  0.4848  +j  cosh  1.986  •  sin  0.4848  * 

=  3.163  +  1.7307, 
and  cosh  7^1  =  3.284  +  1.6667, 

it  follows  from  equation  (58)  that  the  maximum  value  of 
an  alternating  current  arriving  at  the  remote  end  of  the 
6oo-mile  telegraph  line  is 

2  (300  +  4717)  (3.284  +  1.6667)   +  [iS2^ 
Ir  =212.2  -^-     -  2837  +  (300  +  471  7')2  (635  +  n87')io-6] 

(3.163  +  1.7307) 

212.2  ,   . 

=  -  -  -  .  =  0.0169  —  0.02067  ampere, 
5070  +61577 

or  Ir  =  16.9  —  20.67*  rnilBamperes. 

The  absolute  value  of  this  maximum  alternating-current 
value  is  V(i6.9)2  +  (20.6)2  =  26.7  milliamperes,  and  the 
corresponding  unidirectional  current  of  rectangular  wave 
shape  is  |  X  26.7  =  40.1  milliamperes. 
The  potential  difference  across  the  distant  relay  is 

Er   =  IrZr   =    (0.0169   -  0.02067)  (300  +  4717) 

=  14.77  +  i-7^y  v°its. 

*  See  tables  in  Appendix. 


CURRENT  PROPAGATION   IN  LINE   CONDUCTORS     333 


Equation  (30)  now  enables  the  determination  of  the  current 
and  voltage  values  at  the  other  end  of  the  line.     Thus 

Ig  =  (0.0169 —  0.0206  7)  (3. 284  + 1.6667)  +  (I4-77  +  I-7^y) 

(635  +  1187)  (3.163  +  1.730^')  io-* 
=  0.1138  —  0.01457  ampere. 

The  potential  difference  across  the  relay  at  the  generator 
end  of  the  line  is 

IgZt         —         (O.II38         —       0.01457*)         (3OO       +       4717') 

=  41.0  +  49.37  volts, 
and,  therefore,  the  voltage  impressed  upon  the  line  is 

Eg        =       Eg  -       IgZt        =        212.2        -         (41.0       +      49-37) 

=  171.2  -  49.37  volts. 

This  value  may  be  verified  by  means  of  equation  (31). 
The  foregoing  results  are  displayed  graphically  in  Fig.  4, 

V 


49.8 


Fig.  4. 

which  shows  the  harmonic  alternating-current  quantities 
as  vectors,  the  generator  voltage  Egf  being  the  datum  phase. 
The  scale  of  the  receiving-end  quantities  is  5  times  as  large 
as  that  of  the  sending-end  quantities,  all  current  Values 
being  expressed  in  milliamperes.  Absolute  values  and 
phase  relations  are  also  indicated. 


334  TELEGRAPH  ENGINEERING 

Effect  of  Employing  Higher  Signalling  Speeds.  —  If  instead 
of  15  cycles,  the  speed  of  signalling  in  the  foregoing  example 
had  been  ten  times  as  great  as  before,  making  the  dot- 
frequency  of  the  equivalent  alternating  current  150  cycles, 
then  under  otherwise  identical  conditions: 

P  =  942.5, 

/3  =  0.00446, 

a  =  0.00597, 

v  =  157,900  miles  per  second, 

X  =  1052  miles, 
Zr  =  Zt  =  300  +  47107  ohms, 
ysi  =  2.676  +  3.5827, 

and  the  current  traversing  the  remote  relay  is  found  to  be 
Ir  =  i. 08  —  0.4577  milliamperes. 

The  absolute  value  of  this  received  current  is  1.17  milli- 
amperes,  and  the  corresponding  unidirectional  current  of 
rectangular  wave-shape  is  f  X  1.17  =  1.75  milliamperes. 
This  value  is  only  4.3  per  cent  of  that  obtainable  when  the 
signalling  speed  is  one-tenth  as  great.  The  influence  of 
signalling  speed  upon  the  magnitude  of  the  received  im- 
pulses is,  therefore,  evident. 

Direct-current  Transmission  Theory 

9.  Current  in  Leaky  Line  Conductors.  —  When  a  uni- 
directional electromotive  force  is  impressed  upon  a  line 
conductor,  the  current  at  every  point  of  the  line  assumes  a 
steady  value.  Ignoring  the  short  unsteady  period  of  cur- 
rent growth,  the  steady  current  value  at  any  point  on  the 
line  distant  5  from  its  generator  end  may  be  determined 
without  considering  the  effects  of  inductance  and  capacity 
of  the  line  conductor.  The  current  and  voltage  equations 


CURRENT  PROPAGATION   IN   LINE   CONDUCTORS     335 

to  be  satisfied  are  obtained  by  placing  L  =  o  and  C  —  o  in 
equations  (i)  to  (4) ;  whence  for  a  leaky  line 

^H=-RI,  (61) 

I 

T=~SE,  (62) 


§-**• 


and 


(64) 

where  R  is  the  conductor  resistance  per  mile,  and  g  is  the 
leakage  conductance  per  mile  of  conductor  length.  Equa- 
tions (63)  and  (64)  are  identical  equations  which  differ  only 
in  the  terminal  conditions,  and,  therefore,  the  solution  of 
one  will  suffice. 

Choosing  the  former  equation  and  multiplying  both  sides 

by  2  —  ,  there  results 
as 

d?I  dl 
2d?-ds  = 
which,  when  integrated,  becomes 


Replacing  the  constant  of  integration  c\  by  Rgof,  where  cz 
is  also  a  constant,  and  separating  the  variables,  there  re- 
sults 

dl 


336  TELEGRAPH  ENGINEERING 

Another  integration  yields 

loge  [c8  (/  +  VP  +  tf)]  =  VRg.s  =  0s, 

where  c3  is  another  constant  of  integration  and  0 

is  the  attenuation  constant.     In   exponential  form,  this 

equation  becomes 


Squaring,  and  solving  for  7,  gives 


For  convenience  let  -  =  A  +  B  and  c22c3  =  A  —  B\   fur- 

£3 

ther,  let  the  exponential  terms  be  replaced  by  their  equiva- 
lent hyperbolic  functions,  viz.  : 

c±0*  =  cosh/35  ±  sinh/Ss. 
Then  /  =  A  sinh  0s  +  B  cosh  0j.  (65) 

Differentiating  this  expression  with  respect  to  distance 
and  substituting  the  result  in  equation  (62),  there  results 

E=--(A  cosh  0s  +  B  sinh  $s)  .  (66) 

o 

Equations  (65)  and  (66)  are  the  expressions  for  current  and 
voltage  respectively  at  any  point  of  the  line,  but  the  con- 
stants A  and  B  are  still  to  be  evaluated  from  the  terminal 
conditions. 

If  one  source  of  electromotive  force  supplies  current  to 
the  line  and  this  source  be  located  at  one  terminal,  then  the 
constants  A  and  B  may  be  determined  by  placing  5  =  0 
and  representing  the  current  and  voltage  at  this  end  by  I0 


CURRENT   PROPAGATION  IN  LINE   CONDUCTORS     337 

and  EQ  respectively.     Since  cosh  (o)  =  i,  and  sinh  (o)  =  o, 
it  follows  that 


A    -    —      77 


" 


and  B  =  Ig. 

Substituting  these  values  in  equations  (65)  and  (66)  yields 
the  current  and  voltage  respectively  at  any  point  on  the 
line  distant  5  from  its  generator  or  sending  end  as 

/  =  /„  cosh  /3s  -  ^  Eg  sinh  /3s,  (67) 

P 

and  E  =  Eg  cosh  0s  -  -  Ig  sinh  0s.  (68) 

g 

Connecting  a  receiving  instrument  of  resistance  Rr  to 
the  far  end  of  the  line  which  has  a  length  s\t  the  current 
traversing  this  instrument  would  be 


Ir  =  I0  cosh  fa  -E0  sinh  fa,  (69) 

p 

and  the  voltage  across  its  terminals  would  be 

/3 

Er  =  E0  cosh  fa  —  -Ig  sinh  fa.  (70) 

o 

E 

Since  Rr  =  -p  ,  it  follows  that  the  current  entering  the  line 

will  be 

Rr  &  sinh  fa  +  cosh  fa 
I.-E.-B.  -  -  -  .  (71) 

Rr  cosh  fa  +  -  sinh  fa 
g 

If,  as  is  usual,  there  is  a  resistance  at  the  sending  end  also, 
then  Eg  in  the  foregoing  should  be  replaced  by  Eg  — 


338 


TELEGRAPH  ENGINEERING 


where  £/  is  the  voltage  of  the  generator,  and  Rt  is  the  total 
resistance  at  the  generator  end  of  the  line.    Whence 


Rr    sinh  fa  +  cosh  fa 

P 


(Rr  +  Rt)  cosh  fa  +  f-  +  RrRt  f )  sinh  /toi 
\g  /v 


(72) 


Substituting  this  value  in  equation  (69)  gives  the  current 
traversing  the  remote  receiving  instrument  in  terms  of  the 
generator  voltage  as 

EJ 


(Rr+Rt)coshfa 


(73) 


RrRt-)smhpsi 


Ayrton  and  Whitehead  have  shown  that  the  best  re- 
sistance of  a  receiving  instrument  on  a  leaky  telegraph  line 

is  Q 

Rr'  =  -  tanh  fa 
g 

irrespective  of  the  relation  between  the  torque  exerted  and 
the  ampere-turns  applied. 

10.  Illustration  of  Direct-current  Signalling  on  a  Leaky 
Telegraph  Line.  —  Consider  a  simplex  telegraph  circuit 

Rr 


Fig.  S. 

with  a  320-volt  direct-current  generator  at  one  terminal, 
as  shown  in  Fig.  5.    The  line  wire  is  600  miles  long  of  No. 


CURRENT  PROPAGATION  IN  LINE  CONDUCTORS     339 

10  B.  &  S.  gage  copper  wire,  and  a  3oo-ohm  relay  is  con- 
nected at  each  end.     To  determine  the  currents  traversing 
the  relays  for  various  positions  of  the  keys  K  and  K', 
when  the  insulation  resistance  is  0.5  megohm  per  mile. 
In  this  example 

Eg   =320  volts, 
Rt  =  Rr  =  300  ohms, 
R  =  5.28  ohms, 
g  =  2.00  X  IO"6  mhos, 
and  Si  =  600  miles; 


therefore,        ft  =  ^5.28  X  2.00  X  icr6  =  0.00324, 

0si  =  1.944, 
sinh  /3$i  =  3.422, 
cosh/3^  =  3.565, 

|  =  0.000617, 

*  =  1620. 
g 

When  both  keys,  or  their  circuit-closing  switches,  are  closed, 
the  current  entering  the  line  is  obtained  from  equation 
(72)  as 

300  x  0.000617  x  3-422  +  3-565 

600  X  3.565  +  (1620  +  3002  X  0.000617)  3.422 

320  X  4.108 
—  *  --     y     =  0.1706  ampere, 

2139  +  5734 

or  170.6  milliamperes;  and  the  current  that  reaches  the 
other  end  of  the  line  is  obtained  from  equation  (73)  as 

T  320 

/  =  -  —t  -  =  0.0406  ampere, 
2139  +  5734 

or  40.6  milliamperes. 


= 


340  TELEGRAPH  ENGINEERING 

The  closeness  of  this  result  to  that  obtained  in  §  8  by 
means  of  the  alternating-current  method  for  the  same  con- 
ditions and  a  15  cycle  frequency  justifies  the  use  of  the 
direct-current  method  whenever  the  speed  of  signalling  is 
much  below  the  theoretically  attainable  speed1  on  the  line, 
as  with  hand  signalling  on  open  wire  lines.  The  alternat- 
ing-current method  excels  when  dealing  with  long  aerial 
and  underground  cables. 

When  key  Kf  is  opened,  no  current  traverses  the  home 
relay,  but  the  current  flowing  through  the  relay  at  the 
generator  end  of  the  line  is  obtained  from  equation  (69)  by 
placing  Ir  =  o  and  replacing  Eg  by  Egf  —  I0Rt', 

thus     Ig°  cosh  to  =  &  (Egf  -  IgRt)  sinh  to, 
P 

whence  7."  =  E.' 


Rt  sinh  to  +    cosh  to 
g 

or  7f°  = -& .  (74) 

Rt  +  -cothto 
g 

Substituting  the  numerical  values  herein  gives 

T   O  32O 

IB    = =  0.161  ampere. 

300  +  1620  X  1.042 

For  satisfactory  operation,  therefore,  the  relay  at  the 
generator  end  of  the  line  must  be  very  closely  adjusted, 
for  it  should  attract  its  armature  on  170.6  milliamperes 
and  release  it  on  161  milliamperes;  thus  giving  a  margin 
of  9.6  milliamperes.  This  condition  is  improved  by  the 
use  of  generators  at  both  ends  of  the  line,  as  will  now  be 
considered. 


CURRENT  PROPAGATION  IN  LINE   CONDUCTORS     341 

ii.  Simplex  Signalling  with  Generators  at  Both  Line 
Terminals.  —  If  two  equal  cumulatively-connected  sources 
of  current  be  located  one  at  each  terminal  of  a  line,  as  in 
the  usual  simplex  Morse  telegraph  circuit,  then  the  con- 


Fig.  6. 

stants  ^4  and  B  of  equations  (65)  and  (66)  are  evaluated 
upon  a  consideration  of  the  conditions  shown  in  Fig.  6. 
Herein  Eg'  is  the  electromotive  force  of  each  generator,  Rr 
is  the  total  resistance  at  each  terminal  station,  Eg  and  Er 
are  the  potentials  with  respect  to  ground  of  the  line  wire 
at  the  stations  i  and  2  respectively,  and  Ig  and  Ir  are  the 
currents  at  these  stations  respectively. 

When  both  keys  are  closed  as  shown,  the  current  and 
line  voltage  at  station  i  are  obtained  by  placing  s •  =  o  in 
equations  (65)  and  (66)  respectively,  whence 


and  E0=-*-A  =  Egf  -  I0Rr. 

g 

Similarly  the  current  and  line  voltage  at  station  2  are 
obtained  by  placing  5  =  Si  in  the  same  equations,  thus 

Ir  =  A  sinh  fa  +  B  cosh  fa, 
and    Er  =  -  -  (A  cosh  fa  +  B  sinh  fa)  =  -  (£/  - 

o 


342  TELEGRAPH  ENGINEERING 

The  constants  A  and  B  are  ascertainable  from  these  four 
equations,  and  are 

at  \ 

Rr  -  ( i  —  cosh  fa  \  —  sinh  fa 

A  =  EO/ : /v 5\ '     ^ 

2  Rr  cosh  to  +  ( *•  Rr2  +  -  J  sinh  to 
and 

cosh  to  +  Rr  -  sinh  fa  +  i 

B  =  Ea' 77 T\ (76) 

2  Rr  cosh  to  +  ( -  -#r2  +  ~ )  sinh  to 


Substituting  these  values  in  equations  (65)  and  (66)  results 
in  the  current  and  voltage  equations  for  any  point  on  the 
line  distant  s  from  one  end,  when  equal  generators  are 
connected  to  both  ends  of  the  line  wire. 

The  current  traversing  the  relays  at  stations  i  and  2  are 
respectively 

Ig  =  B, 
and  Ir  =  A  sinh  fa  +  B  cosh  fa 

as  already  indicated.  Upon  replacing  A  and  B  herein  by 
their  equivalents  given  in  equations  (75)  and  (76),  these 
currents  are  found  to  be  equal,  as  might  be  inferred  from 
the  symmetry  of  the  line  and  terminal  conditions,  and  have 
the  value 

cosh  fa  +  Rr-  sinh  fa  +  i 

(77) 


2  Rr  cosh  fa  +  (  lRr2  +  -  )  sinh  fa 
\p  gl 


When  one  of  the  keys  is  opened  the  current  traversing  the 

relay  at  the  other  terminal  station  is  given  by  equation  (74). 

To  illustrate  the  advantage  of  dividing  the  total  voltage 


CURRENT  PROPAGATION  IN   LINE   CONDUCTORS     343 


on  a  telegraph  line,  one-half  being  impressed  at  each  end, 
consider  the  same  circuit  as  was  discussed  in  the  preceding 
article.  In  this  case  a  1 60- volt  generator  is  located  at  each 
end  of  the  6oo-mile  line. 

The  current  traversing  each  relay  when  both  keys  are 
closed  is  given  by  equation  (77)  as 

I  _/r-i6o          3-565+300X0.000617  X  3422  +  i 

2X300X3. 565  +  (0.00061 7X30?  +1620)3.422 
=  0.1056  ampere  =  105.6  milliamperes, 

while  the  current  traversing  a  relay  when  the  key  at  the 
opposite  station  is  opened  is  given  by  equation  (74)  as 

ro      160 

ig    =  ~  -  =  0.0805  ampere 

300  -f  1620  X  1.042 

=  80.5  milliamperes. 

The  comparison  of  the  two  generator  arrangements  for 
the  line  under  consideration  is  revealed  in  the  following 
table,  the  current  values  being  expressed  in  milliamperes. 
It  is  seen  that  with  a  generator  at  each  end  the  operating 
margin  is  25.1  milliamperes,  as  against  9.6  milliamperes 
at  the  home  relay  for  a  single  generator  of  double  voltage 
at  the  home  end  of  the  line. 


Key  positions 

32O-volt  generator 
at  home  end 

i6o-volt  generators 
at  both  ends 

Current 
through 
relay  at 
generator 
end 

Current 
through 
relay  at 
distant 
end 

Current 
through 
relay  at 
home 
end 

Current 
through 
relay  at 
distant 
end 

Both  keys  closed  

170.6 

161 

0 

40.6 
O 

o 

105.6 
80.5 
o 

105.6 
O 

80.5 

Distant  key  open  

Home  key  open  

Operating  Margin  

9.6 

40.6 

25-1 

25-1 

344  TELEGRAPH   ENGINEERING 

12.  Duplex  and  Quadruplex  Signalling.  —  The  theory 
of  signalling  on  leaky  lines  discussed  in  the  preceding  pages 
is  also  applicable  to  duplex  and  quadruplex  telegraph  cir- 
cuits if  the  terminal  conditions  are  properly  deduced. 
The  general  expressions  for  current  and  voltage  are  equa- 
tions (65)  and  (66),  wherein  the  constants  A  and  B  depend 
upon  the  conditions  existing  at  the  ends  of  the  line  wire. 
The  values  of  these  constants  with  duplex  and  quadruplex 
signalling  are  different  from  those  pertaining  to  simplex 
signalling,  already  considered. 

In  a  polar  duplex  circuit,  let  Rp  =  entire  resistance  of 
each  polarized  relay,  Rb  =  resistance  of  each  battery  or  of 


Relay 
Fig.  7. 

the  protective  resistance  in  series  with  each  generator,  and 
r  =  resistance  of  each  artificial  line,  as  indicated  in  Fig.  7 
for  one  station.  Placing  s  =  o  in  equations  (65)  and  (66), 
there  results 


and  E=  -.A  = 


. 

where  -  -  =  q  for  simplicity.     The  current  and 


CURRENT  PROPAGATION  IN  LINE   CONDUCTORS     345 

voltage  conditions  at  the  other  end  are  obtained  by  placing 
s  =  Si,  whence 

Ir  =  A  sinh  0Si  +  B  cosh  Qsi, 

and£r  =  --U  cosh  fa  +  5  sinh  0*)=  ±  (qEgf  -  Ir 

the  plus  sign  being  taken  when  the  two  batteries  or  genera- 
tors oppose  each  other  as  when  both  pole-changers  are 
either  idle  or  energized,  and  the  negative  sign  being  taken 
when  the  two  current  sources  assist  each  other  as  with  only 
one  pole-changer  energized.  These  expressions  assume  the 
current  traversing  the  artificial  lines  to  remain  constant 
irrespective  of  key  movements. 

Solving  for  A  and  B  from  the  preceding  four  equations, 

yields  R     q 

-  cosh  Qsi  db  —2  •  -  sinh  fa  ±  i 

B  =  *E''l  -  \R  -  2   /     z  R  2     8\  -  '  (78) 
[±  i  -  i.pcoshto  +(±f  .£*  -eWnhto 
V  /  2  \     0     4       gl 

and  A=£B-qE0'  (79) 


The  upper  signs  in  equation  (78)  are  employed  when  the 
generators  oppose  and  the  lower  signs  are  used  when  the 
generators  assist  each  other.  Substitution  of  these  values 
in  equations  (65)  and  (66)  gives  the  final  expressions  for 
current  and  voltage  in  the  case  of  a  polar-duplex  telegraph 
circuit. 

The  bridge  duplex  and  the  quadruplex  terminal  condi- 
tions may  be  similarly  analyzed  and  the  current  and  voltage 
equations  formed.*  It  is  to  be  noted  that  the  current 
passing  through  the  relay  of  a  bridge  duplex  circuit  ex- 

*  An  excellent  treatment  'of  these  conditions  appears  in  a  paper  by 
F.  F.  Fowle  on  "Telegraph  Transmission,"  Trans.  A.I.E.E.,  v.  30,  p.  1683. 


346  TELEGRAPH  ENGINEERING 

pressed  in  terms  of  the  current  Ig  at  the  end  of  the  line 
wire  and  the  voltage  Eg'  of  the  generator  is 

T  aEgf  -aIg(2Rb  +  r  +  a)  (    . 

^- 


where  P  is  the  resistance  of  the  relay,  a  =  resistance  of 
each  half  of  the  retardation  coil,  r  =  resistance  of  artificial 
line,  and  Rb  =  resistance  in  series  with  generator. 

PROBLEMS 

1.  Determine  the  attenuation  and  wave-length  constants  of  a 
perfectly-insulated  ground-return  line  having  the  following  constants 
per  mile,  when  the  frequency  of  the  impressed  electromotive  force  is 
50  cycles:   R  =  4.25  ohms,  L  =  0.002  henry,  and  C  =  0.016  micro- 
farad. 

2.  Compute  the  current  and  voltage  at  both  ends  of  an  8oo-mile 
line  of  No.  10  B.  &  S.  gage  copper  wire  and  having  a  3oo-ohm  relay 
at  each  end.     A  150- volt  i5-cycle  alternating-current  generator  is 
to  be  considered  connected  in  one  terminal  of  this  simplex  circuit  in 
place  of  a  3  20- volt  direct-current  generator.     The  constants  of  the 
relay  and  line  are  those  given  in  §  8.     Construct  the  vector  diagram 
of  currents  and  electromotive  forces. 

3.  Verify  the  value  of  Ir  given  in  §  8  for  signalling  on  a  particular 
line  at  a  speed  corresponding  to  a  dot-frequency  of  150  cycles. 

4.  For  different  key  positions,  determine  the.  unidirectional  cur- 
rents traversing  the  25o-ohm  terminal  relays  on  a  4oo-mile  simplex 
telegraph  line  of  No.  9  B.  &  S.  gage  copper  wire.    Assume  the  line  to 
have  an  insulation  resistance  of  0.5  megohm  per  mile,  and  that  a 
single    i6o-volt   direct-current   generator  located  at   one   terminal 
station  supplies  current  to  the  circuit. 

5.  Calculate  the  currents  traversing  the  relays  of  the  line  men- 
tioned in  the  preceding  problem  when  the  1 60- volt  generator  is  re- 
placed by  two  8o-volt  generators,  one  at  each  line  terminal. 

6.  Solve  Problem  3  of  Chap.  II,  taking  into  account  a  uniformly 
distributed  leakance  of  io~6  mhos  per  mile  for  this  475-mile  polar 
duplex  circuit. 


CHAPTER  XI 

SUBMARINE  TELEGRAPHY 

i.  Theory  of  Cable  Telegraphy.  —  Because  of  the  large 
capacity  and  small  leakance  of  submarine  telegraph  ca- 
bles, the  direct-current  transmission  theory 'discussed  in 
the  foregoing  chapter  is  inapplicable  to  signalling  over 
cables.  However,  the  alternating-current  transmission 
theory  already  considered  may  be  utilized  for  cable  teleg- 
raphy if  the  speed  of  signalling  is  such  that  a  steady  state 
is  constantly  approached  within  a  reasonable  margin.  For 
practicable  speeds  on  commercial  cables  this  theory  is 
limited  to  cable  sections  of  moderate  length.  When  the 
steady  state  is  not  nearly  approached  during  each  signal, 
then  the  growth  and  fall  of  the  direct-current  accompany- 
ing the  application  and  withdrawal  of  constant  voltage  to 
one  end  of  the  cable  are  alone  of  importance.  The  con- 
sideration herein  presented  of  these  transitional  states  on 
long  cables,  conveniently  called  the  transition  theory  of 
transmission,  will  reveal  the  nature  of  the  current  which 
reaches  the  distant  terminal  of  the  cable. 

If  a  steady  voltage  E  is  applied  to  one  end  of  a  perfectly- 
insulated  cable  of  length  /,  while  the  other  end  is  grounded, 
the  potential  at  each  point  gradually  rises  until  its  value 
at  any  poiht  distant  5  from  the  sending  end  is 

*  ...  ;    EJ  =  E1-^,         \  (i) 

347 


348          TELEGRAPH  ENGINEERING 

which  indicates  that  the  voltage-distance  graph  for  the 
steady  condition  is  a  straight  line  falling  from  E  to  zero, 
as  shown  in  Fig.  i.  Should  this  condition  be  altered,  say 


IB 
•i 


Fig.  i. 

by  grounding  the  sending  end,  then  the  voltage  there  at 
that  instant  would  be  zero,  but  at  other  places  in  the  cable 
would  be  as  indicated  by  equation  (i).  The  subsequent 
voltage  at  any  point  is  found  by  drawing  an  image  of  AB 
toward  the  left,  forming  a  curve  DAB,  and  considering 
this  curve  to  represent  a  periodic  function  of  distance; 
which  is,  therefore,  expressible  by  a  Fourier's  series  of  the 
form 

Em  =  F04-Fisin0  +  F2sin20  +  .  .  .  +FnsinnO  + 
GI  cos  0  +  Gz  cos  20  +  .  .  .  +  Gn  cos  nO, 

where  6  =  —  and  n  is  any  integer.  To  evaluate  the  co- 
efficients, multiply  both  members  by  sin  nO  times  the  width 
ds  of  the  element  and  summate  these  elementary  areas  over 
the  distance  DB,  and  there  results 

ri  /»2J  (*1l 

Emf  sin  nO  ds  =  F0  I     sin  nS  ds  +  FI  I    sin  0  •  sin  n0  ds 
Jo  Jo 

(*2l 

+  •  •  •   +  Fq  I    sin  qB  •  sin  nB  ds  +  •  •  - 
Jo 

ri  rzi 

sin2  ndds  +  GI  I    cos  0  -  sin  nB  ds  +  •  •  • 
Jo 

X2l  f*2l 

cos  q6  •  sin  nd  ds  +  •  •  •  +  Gn  I    cos  nB  •  sin  nd  ds. 
Jo 


SUBMARINE   TELEGRAPHY  349 

Since    Emr  =  E  —  -  E,  dO  =  y  ds,  and  when  s  =  2  1  then  0  =  2  TT, 
I  I 

E  I      smnedO  --  I      6  sin  nd  dO  =  FQ  I      sin  n6  d0 

JQ  ffJ  JQ 

X27T  /*2tr 

sin  0  •  sin  w0  </0  +  •  •  •  +  Fq  I      sin  g0  •  sin  w0  d0 
t/O 

+  .  -  -  +Fn  l&xPntidO  +  Gi  /     cos0-sinw0</0  +  -  -  • 
Jo  Jo 

+  Gq  I   *cosq0  •smn8dO+  •  •  •  +Gn  I     cos  n6  •  sin  nd  d6. 
The  terms  of  this  expression  are  integrated  as  follows: 


T2'  . 

I      sin  n0  dO  =  \  =  o. 

Jo  \_    n    J0 


rif  Tj  Q  ~|2ir  2 

^  sin  w^  c?0  =    -r  sin  w^  --  cos  w^       =  --- 
L^2  w  Jo         -    n 

I      sLnqO'SmnOdO  =  -  I       cosfg—  n\B  —  cos(q  +  n\d  \dO 

=  i  fsin  (q  -  n)  0  _  sin  (q  +  n)  0"]2y 
2L     g  —  »  g  +  w     Jo 

When  q  and  w  are  different  integers,  substitution  of  the 
limits  reduces  this  expression  to  zero. 

rsin2  nBde  =  -  I      (i  —  cos  2  n0  }  dd 
2Jo     V  / 

i  f\      sin  2  w^12T 

=  -  \e  --        =  TT. 

2[_  2W      Jo 

I      cosqO  'SmnddO  =  -  I      Isinln  +  qjd  +  smln—  q\6  \dO 

_  _  i  fcos  (^  +  q)  0  ,  cos  (n  —  q)  0"[2r 
2L     w  +  g  w-        1 


350  TELEGRAPH  ENGINEERING 

This  expression  is  zero  whether  the  integers  q  and  n  are 
equal  or  unequal.  Therefore,  by  substitution, 

2E  2E 

—  =  irFn  or  Fn  = — , 
n  irn 

and  consequently  the  potential  at  any  point  of  the  cable 
distant  s  from  the  sending  end  where  E  volts  are  impressed, 
reaches  the  maximum  value  of 

Emf   =  —  ( Sm  0  +  -  Sin  2  0  +     •    •     •     +  - 

TT   \  2  n 

•n   f         2  j 

or       Em  =  — 

This  equation  represents  the  voltage  distribution  at  the 
instant  of  grounding  the  sending  end  of  the  cable. 

If,  now,  the  potential  distribution  be  left  to  itself,  then 
the  diminishing  voltage  all  along  the  cable  must  satisfy 
the  differential  equation  of  propagation  over  a  uniform  line, 
namely,  equation  (4)  of  Chap.  X,  which  is 


where  C,  L,  g  and  R  are  the  cable  constants  per  unit  length. 
But  in  submarine  telegraphy  the  inductance  of  cables  is 
very  small  and  the  leakage  conductance  is  very  low,  that 
is,  L  and  g  are  negligibly  small;  so  that  the  equation  to  be 
satisfied  reduces  to 


dt 

the  so-called  "telegraph  equation." 
A  solution  of  this  equation  suggests  itself  of  the  form 


SUBMARINE   TELEGRAPHY  351 

where  E'  is  the  voltage  at  the  point  distant  s  from  the  send- 
ing end  at  a  time  /  after  grounding  that  end.  Differenti- 
ating this  expression  twice  with  respect  to  distance  there 


results jsT^'j  an(^  differentiating  with  respect  to  time 

there  results  -  n2bE'.     Substituting   these   values  in   (4) 
yields 

'  =-RCn2bE': 


whence  b  =  —.  (6) 


With  this  interpretation  of  the  exponential  constant, 
equation  (5)  is  a  solution  of  equation  (4),  for  it  reduces  to 
equation  (2)  when  /  =  o,  is  zero  when  /  =  <x>  ,  and  is  zero 
when  s  =  o  or  s  =  I. 

The  fall  in  voltage  at  the  point  of  reference  during  the 
time  /  elapsing  since  suppression  of  voltage  E  at  sending 
end  by  grounding  is 


<»> 


On  the  other  hand,  if  the  origin  of  time  were  taken  at  the 
instant  when  the  voltage  E  is  applied,  the  rise  in  voltage 
during  the  time  /  at  the  point  of  reference  is  also  given  by 
equation  (7).  This  expression  also  satisfies  equation  (4) 
since  it  is  the  difference  of  two  expressions  which  satisfy 
it  separately. 

The  growth  of  current  in  the  cable  at  the  point  under 
consideration  is  obtained  by  differentiating  (7)  with  respect 
to  distance,  and  using  de'  =  —  R  ds  •  /'.  Thus,  the  current 


352  TELEGRAPH  ENGINEERING 

value  at  a  time  /  after  applying  the  voltage  E  to  the  sending 
end  is 


At  the  receiving  end  s  =  /,  and  the  current  is 

//  =  —  T—  <  2  COS  HIT  —  2J  ( €~n26'  COS  WTT  J  >  • 

But  2/cosw7r=—  i  +  i  —  i  +  i—  •  •  •  ; 

transposing  the  first  term  of  the  right  hand  member,  there 
results 

i  +  2  cos  HTT  =  i  —  i  +  i  —  i+  •  •  •  , 

and  adding  these  two  series  term  by  term  it  will  be  found 
that 


cos  rnr  =  —    . 

n=l 


Consequently,  the  instantaneous  current  at  the  grounded 
receiving  end  is 


when  both  ends  of  the  cable  are  without  sending  or  receiving 
instruments.     The  series 


and  when  t  is  zero,  the  sum  is  —  i  +  i  —  i  +  •  •  •   =—  J 
as  before,  and  therefore  //  is  zero  when  time  begins. 

As  the  foregoing  expression  for  //  is  slowly  convergent 
for  small  values  of  /  it  is  more  convenient,  for  purposes  of 


SUBMARINE  TELEGRAPHY 


353 


evaluating  the  received  current  at  first,  to  alter  its  form  into 
a  rapidly-converging  series  by  means  of  an  equality  due  to 
Fourier  that 


oo  n^r 

2«"?cos^ 

n=l 


8000 
7500 


7000 
6500 


6000 
6500 


£  5000 
E4500 


3500 
3000 


2500 
2000 


1500 
1000 


ARRIVAL  CURVES 

on 
2500   Mile  Cable 


\ 


500 


0    0.2    0.4  0.6   0.8     1 


2 

Seconds 


Fig.  a. 


Taking  bt  =  ^  and  —  "  =  i,  equation  (9)  becomes 


*  Sir  WiUiam  Thomson,  "  Collected  Papers,"  V.  2,  p.  48;  1884  ed. 


354  TELEGRAPH  ENGINEERING 

then  using  equation  (6),  there  results 

oo        -  (2  m  +  1)  V2 

"'    •         <»> 


If  the  key  be  kept  depressed,  the  current  at  the  receiving 

jy 

end  will  grow  from  o  for  /  =  o  to  the  value  •—  ,  as  obtained 

Kl 

from  (9)  by  placing  /  =  oo  .  The  graph  of  current  growth 
will  resemble  curve  7,  Fig.  2.  When  the  battery  is  re- 
moved and  the  sending  end  grounded,  the  current  at  the 
other  end  will  decay  as  shown  by  curve  II,  which  is  the 
same  as  curve  /  drawn  downward  from  the  steady  current 
value  as  axis. 


2.  Illustration  of  Current  Growth  at  the  Receiving  End 
of  a  Cable.  —  As  an  example  of  the  growth  of  the  current 
at  the  receiving  end  of  a  cable,  consider  a  25oo-mile  cable 
having  a  total  resistance  of  5000  ohms  and  a  total  capacity 
of  987  microfarads  to  have  40  volts  impressed  upon  the 
sending  end.  Thus,  Rl  =  5000  ohms  and  Cl  =  0.000987 

7T2 

farad;     therefore    b  = —  =  2.00,   and   the 

5000  X  0.000987 

ultimate  current  value -at  the  grounded  receiving  end  of  the 
cable  is  0.0080  ampere.  Values  of  //  to  an  accuracy  of  a 
fraction  of  one  per  cent  can  be  obtained  by  using  only  the 
first  terms  of  equations  (9)  and  (10),  if  the  latter  be  used 
for  time  intervals  up  to  one  second,  say,  and  the  former 
for  longer  intervals.  For  the  conditions  of  this  example, 
the  equations  utilized  are 

//  =  aE\f^.~&.?2^e~^empea»toit<  i, 

f    7T/U  V  t 


SUBMARINE  TELEGRAPHY 


355 


and 

//  =  7T7(i  -  2  e~bt}  =  0.008  (i  -  2  €~2t]  amperes  for/  >  i. 
Rl  \  I  \  I 

The  values  of  current  at  the  receiving  end  of  this  cable  as 
calculated  from  these  expressions  (see  table  of  exponential 
functions  in  Appendix)  for  different  values  of  t  are  given  in 
the  following  table,  and  are  also  shown  by  curve  7  of  Fig.  2. 
It  will  be  observed  that  the  application  of  voltage  to  one 
end  of  a  cable  produces  an  instantaneous  effect  at  the  other, 
but  the  growth  of  current  at  first  is  so  extremely  slow  as  to 
give  rise  to  the  impression  that  there  is  at  first  a  "  silent 
interval." 


t 

seconds 

// 
microamperes 

t 
seconds 

IT 

microamperes 

O 

O 

0.8o 

4794 

0.05 

0.0000017 

0.90 

5357 

0.10 

0.279 

I.OO 

5835 

0.15 

14.96 

1  .20 

6548 

O.2O 

93-6 

1-50 

7204 

0.25 

288 

1.70 

7466 

0.30 

599 

2.OO 

7707 

0.40 

1457 

2.50 

7892 

0.50 

2401 

4.OO 

.  7995 

O.6O 

3302 

10.00 

7999 

0.70 

4112 

00  . 

8000 

3.  Transmission  of  Telegraphic  Signals.  —  The  alpha- 
betic code  used  generally  for  cable  telegraphy  is  the  con- 
tinental Morse  Code,  comprising  for  its  characters  various 
combinations  of  dots  and  dashes  as  tabulated  in  §  7  of 
Chap.  I.  The  transmission  of  a  letter  is  usually  accom- 
plished by  repeated  applications  of  constant  potential  for 
equal  intervals  of  time  to  one  end  of  the  cable,  the  potential 


TELEGRAPH  ENGINEERING 

differing  in  direction  for  dots  and  for  dashes.  With  this 
method  of  signalling  over  cables  the  code  for  alphabet  and 
figures  is  better  represented  as  below,  dots  and  dashes  being 
indicated  respectively  by  upwardly  and  downwardly  pro- 
jecting rectangles  of  equal  length. 


c  ~d  e  f 


T  •  ••-•I  M       -     Hi  ••  ••     M  M 


o  P  Q  r  s  t 


Dashes 
v  w  x  y  z 


12  34 


5  6  7 


9  0  or         0 


Taking  T  seconds  as  the  duration  of  a  dot  or  dash  element, 
the  interval  between  elements  is  generally  r,  that  between 
letters  3  r,  and  that  between  words  7  T.  By  an  analysis 
of  traffic  matter  it  is  found  that  the  average  letter  contains 
7.2  elements,  including  space  between  letters,  and  hence 
requires  7.2  r  seconds  for  transmission. 

Signals  are  usually  sent,  therefore,  as  a  succession  of 
equal  rectangular  voltage-time  pulses  differing  in  direction 
and  spaced  irregularly.  If  the  alternating-current  theory 
of  wave  propagation  were  applied  to  cable  signalling,  two 
hypothetical  frequencies  for  an  equivalent  sine  wave  would 
be  recognizable,  namely:  the  dot-frequency,  as  outlined 
in  the  foregoing  chapter,  and  the  reversal-frequency,  as 


SUBMARINE  TELEGRAPHY 


357 


indicated  in  Fig.  3;  the  former  being  twice  as  high  as  the 
latter.  Kennelly*  has  considered  both  frequencies  in 
ascertaining  the  best  resistance  of  receiving  instruments 
on  cables,  and  the  influence  of  terminal  apparatus  upon 
signalling  speed.  He  has  shown  that  the  receiving  instru- 


J. 

\ 

Seconds 

/ 

f 

*\ 

\ 

r 

Fig.  3- 

ment  for  greatest  sensitiveness  should  have  a  resistance 
equal  to  the  resistance  component  of  the  surge  impedance 
of  the  cable  plus  the  resistance  component  of  reactive 
apparatus,  if  any,  in  the  receiving  circuit.  The  surge 
impedance,  from  §  4  of  Chap.  X,  being  in  general 

f~+ja 


g  +JPC 


or 


v/f 


+JPL 

g+jpc' 


rjr 

becomes  y  —  ohms  for  highly  insulated  cables,  where 

p  =  2  TT  times  the  frequency  (dot-  or  reversal-frequency  as 
selected)  of  the  equivalent  alternating  current.  Thus, 
taking  a  reversal-frequency  of  4  cycles  per  second  in  the 
numerical  illustration  of  §  2,  and  with  no  reactive  apparatus 
at  the  receiver,  the  best  resistance  of  the  winding  of  the 
receiving  instrument,  as  found  by  this  method,  is  the  re- 
sistance component  of 

*  "  Hyperbolic  Functions  applied  to  Electrical  Engineering,"  1912,  Chap.  9. 


358          TELEGRAPH  ENGINEERING 


2  7T 


=  V202,ooo  (90°)  =449  (45°) 


2500 

or  is  449  cos  45°  =  317  ohms. 

Reverting  to  the  transition  theory  of  cable  transmission,  a 
dot  or  dash  may  be  transmitted  by  applying  a  unidirectional 
voltage  at  the  sending  end  of  the  cable  for  T  seconds, 
thereafter  grounding  that  end;  consequently  the  equation 
for  a  dot  or  dash  is  obtained  by  subtracting  from  equation 
(9)  a  similar  equation  in  which  the  time  /  is  replaced  by 
t  —  T  whence 


COS  HIT     - 


In  other  words,  a  dot  is  transmitted  by  the  maintenance 
of  voltage  at  the  sending  end  for  an  infinite  time,  and  after 
T  seconds  the  application  of  an  equal  opposite  potential 
also  maintained  indefinitely.  The  subtraction  indicated 
in  equation  (n)  is  most  conveniently  done  graphically. 
The  curve  of  arrival  of  a  dash  element  for  a  contact  lasting 
o.i  second  on  the  cable  considered  in  the  foregoing  numeri- 
cal illustration  is  shown  by  curve  7  of  Fig.  4  as  the  sum  of 
curves  a  and  b.  An  enlarged  view  of  this  curve  is  shown 
by  curve  T,  the  multiplier  being  5.  It  will  be  evident  that 
the  shorter  the  contact  the  lower  and  flatter  will  be  the 
curve  of  received  current  for  a  dot  or  dash  element. 

By  applying  the  foregoing  method  it  is  a  simple  matter 
to  construct  a  curve  showing  the  received  instantaneous 
current  for  any  combination  of  dots  and  dashes.  It  is  only 
necessary  to  plot  the  same  dash  arrival  curve  in  the  proper 
places  and  with  proper  direction  and  then  add  the  ordinates. 


SUBMARINE  TELEGRAPHY 


359 


Thus  in  Fig.  4  are  also  shown  the  forms  of  received  signals 
on  this  cable  for  the  letters  E,  N,  D,  B  and  BT,  the  lower 
dotted  lines  representing  the  nature  of  the  impressed  elec- 


0     0.1  0.2    0.3   0.4  0.5  0.6  0.7  0.8    0.9   1.0   1JL    1.2   1.3    1.4  1.5  1.6   1.7   1.8   1.9  2.0 
Seconds 

Pig.  4. 

tromotive  force.     Curve  II  exhibits  the  cumulative  action 

of  successive  like  signals  for  a  signalling  speed  of — 

7.2  X  o.i 

=  83.3  letters  per  minute  and  the  result  is  apparently 
undecipherable,  but  still  it  would  be  legible  to  an  expert 
recorder  attendant. 
In  Fig.  5  is  shown  the  received  current  curve  for  the 


3<5° 


TELEGRAPH  ENGINEERING 


same  letters  BT  sent  at  the  same  speed  on  a  shorter  cable 
having  the  same  constants  per  unit  length  as  that  pre- 
viously considered.  The  variations  in  this  curve  are  very 
prominent  and  are  easily  interpreted. 


10000 
8000 
6000 
4000 
2000 
0 
2000 
4000 
6000 
8000 
0 
( 

£1 

^ 

\ 

LETTERS  BT  Received 
on 
1250  Mile 
Cable 

1 

\J 

\ 

2 

\J 

\ 

/ 

\ 

£ 

\ 

\ 

/    ^ 

^ 

*.~— 

\ 

s* 

\ 

P 

\ 

7 

\ 

f 

\ 

/ 

t- 

/ 

\> 

- 

Dots 

V 

Dashes 

T 

)       0.1      0.2      0.3      0.4      0.5     0.6     0.7      0.8      0.9      1.0      1.1      1.2      1.3      1.4      1. 
Seconds 

Fig. 


The  receiving  instrument  used  in  cable  telegraphy  over 
relatively  short  distances  (several  hundred  miles)  is  the 
ordinary  sensitive  relay,  while  over  long  distances  the 
siphon  recorder  is  used.  The  siphon  recorder,  devised  by 
Lord  Kelvin  in  1867,  traces  on  a  paper  tape  the  curve 
of  current  which  traverses  the  instrument  winding.  This 
recorder  is  a  D'Arsonval  galvanometer,  the  movements 
of  the  coil  of  which  are  transmitted  by  means  of  two  silk 
fibres  to  an  extremely  small  glass  siphon.  As  one  end  of 
this  siphon  passes  transversely  to  and  fro  across  the  slowly- 


SUBMARINE  TELEGRAPHY 


361 


moving  tape,  it  takes  ink  at  the  other  end  from  a  small 
reservoir  and  exudes  it  upon  the  paper  in  the  form  of  a 
wavy  line.  To  eliminate  friction,  the  siphon  is  kept  vibrat- 
ing rapidly,  by  means  of  an  electromagnetic  vibrator,  so 
as  to  oscillate  perpendicularly  to  the  paper,  thereby  form- 
ing a  trace  that  really  consists  of  a  succession  of  closely 


Fig.  6. 

spaced  dots.  Fig.  6  shows  a  siphon  recorder  made  by 
Muirhead  &  Co.,  Ltd.  The  suspension  piece  with  vibrator 
is  shown  in  Fig.  7. 

Fig.  8  is  a  reproduction  to  exact  size  of  a  portion  of  a 
message  which  was  transmitted  over  the  Bay  Roberts,  N.  F.- 
New  York  i6io-mile  cable  at  a  speed  of  200  letters  per 


362  TELEGRAPH  ENGINEERING 

minute  ( r= =  0.0416  second V     The  dotted  neu- 

'    V          200  X  7.2  / 

tral  line  shows  that  the  siphon  recorder  in  practice  does 
not  behave  as  a  fixed-zero  instrument. 

The  resistance  of  siphon  recorders  is  usually  between  300 
and  800  ohms,  and  their  inductance  about  0.2  to  0.3  henry. 


Fig.  7. 

The  recorder  will  operate  satisfactorily  on  a  current  as 
small  as  20  to  40  microamperes. 

Signals  are  sent  either  manually  or  by  means  of  auto- 
matic transmitters  such  as  described  in  §  i  of  Chap.  IV. 
Fig.  9  shows  a  cable  key  with  removable  contact  levers. 
Automatic  transmission  by  means  of  perforated  tapes 
results  in  greater  speed  and  more  regularity  in  the  signals 
than  is  possible  with  hand  transmission;  it  is  the  method, 
therefore,  chiefly  employed  in  cable  telegraphy.  « 


SUBMARINE  TELEGRAPHY 


363 


4.  Speed  of  Signalling.  —  From  the  foregoing  expres- 
sions it  will  be  seen  that  the  received  current  is  a  function 
of  bt,  consequently  the  time  required  to  establish  a  given 
current  at  the  far  end  varies  inversely  with  b  or  directly 


One        hund      red          f      orty          th       ree 


hr^M\r^^r^^^ 


Federal  St.  Boston       Mass 

Fig.  8. 

CRF 
with—  —  .     Since  the  speed  of  signalling  varies  inversely 

with  the  time  required  for  establishing  the  necessary  cur- 
rent, this  speed  varies  directly  with         ,  or  it  varies  in- 


Fig.  9. 


versely  with  the  product  of  the  total  resistance  and  total 
capacity  of  the  cable.  Also,  when  C  and  R  are  kept  con- 
stant, the  speed  of  signalling  varies  inversely  with  the  square 
of  the  cable  length. 


364  TELEGRAPH  ENGINEERING 

Accordingly,  the  speed  of  signalling  over  a  given  distance 
may  be  increased  by  decreasing  the  total  capacity  or  the 
total  resistance  or  both.  The  capacity  depends  upon  the 
conductor  diameter,  upon  the  distance  between  conductor 
and  metallic  sheath  and  upon  the  dielectric  constant  of  the 
cable  insulation.  Greater  separation  between  conductor 
and  armor  and  the  use  of  larger  wire  are  accompanied  by  an 
increase  in  cost.  Further,  with  very  few  exceptions,  no 
insulating  material  having  a  lower  dielectric  constant  than 
gutta  percha  compound  has  been  successfully  used  up  to 
the  present  time  in  submarine  cables. 

The  statement  that  the  speed  of  signalling  varies  inversely 
with  the  product  of  total  resistance  and  total  capacity  of  a 
cable  is  called  the  "CR  Law  "  and  was  announced  by  Lord 
Kelvin.  In  other  words,  two  cables  of  length  /i  and  k 
having  the  constants  Ci,  RI  and  C2,  R?.  respectively  will  be 
similar  (that  is,  yield  the  same  arrival  curves  "under  identi- 
cal conditions)  when 

CM?  =  cAif.  (12) 

This  is  only  true  when  the  cable  is  entirely  devoid  of  in- 
ductance and  leakance,  has  no  terminal  apparatus,  and 
is  earthed  at  both  ends.  Malcolm  has  shown  that  two 
cables  having  the  constants  Ci,  Zi,  RI,  gi  and  C2, £2,  R^  £2 
and  with  terminal  apparatus  of  impedances  Zti,  Zri  and  Z<2, 
Zr2  at  transmitting  and  receiving  ends  respectively  will  be 
similar  when 

gih  _  Zti  _  Zri  __  /    x 

gili      Zt2      Zrf 

and  the  size  of  the  signals  will  be  in  the  ratio  of  rj  to  i. 
This  generalized  expression  may  be  appropriately  called 
Malcolm's  law.  It  reduces  to  equation  (12)  when  the 


SUBMARINE  TELEGRAPHY  365 

cable  inductance  and  leakance  and  the  terminal  apparatus 
are  ignored. 

Fig.  4  shows  the  graph  of  current  received  over  a  2500- 
mile  cable  without  terminal  apparatus  for  the  letters  BT 
with  contacts  of  o.i  second.  Taking  7.2  elements  for  an 
average  letter  including  space,  the  number  of  five-letter 
words  transmitted  per  minute  over  this  cable,  having 
CRl2  =  4.935  ohm-farads  or  seconds,  under  these  conditions 

60 
would  be -  =  15.     Signalling  at  this  speed 

gives  legible  results,  as  evinced  by  the  figure.  The  greater 
legibility  for  the  same  signalling  speed  over  a  shorter  cable 
is  manifest  from  Fig.  5  for  CRl?  =  1.234  seconds.  The 
maximum  speed  of  signalling  over  any  cable  is  determined 
by  constructing  arrival  curves  of  various  words  using  dif- 
ferent values  of  r  and  submitting  these  to  an  experienced 
operator  to  determine  the  limit  of  legibility.  On  short 
cables  the  inertia  of  the  receiving  instrument  prevents  the 
attainment  of  the  theoretically  possible  speed  of  trans- 
mission. 

The  use  of  condensers  in  series  with  a  cable  at  one  or 
both  of  its  ends  affords  better  definition  in  the  received 
signals.  The  curves  of  Fig.  10,  calculated  according  to  a 
method  given  by  Malcolm,*  show  the  arrival  curves  for  the 
same  cable  considered  in  the  foregoing  numerical  illustra- 
tion, with  terminal  condensers.  Curve  /  represents  the 
received  current  curve  when  a  condenser  of  gV  the  capacity 
of  the  cable  is  connected  in  series  with  the  cable  at  one  end. 
Curve  //  represents  the  current  curve  when  a  condenser  of 
-j1^-  the  capacity  of  the  cable  is  connected  at  each  end.  This 
curve  is  considerably  lower  than  the  first  but  its  decay  is 
*  The  Electrician,  V.  69,  pp.  315-318  and  981. 


366 


TELEGRAPH   ENGINEERING 


much  more  rapid.  The  advantage  of  introducing  a  con- 
denser of  ^  the  capacity  of  the  cable  in  series  with  it  at 
its  middle  point,  if  possible  from  a  practical  viewpoint,  is 
shown  by  curve  ///.  The  ultimate  steady  current  value 
for  all  of  these  conditions  is  zero. 


800 
720 
640 
560 

r 

E  400 
|  320 
240 
160 
80 

^ 

•  —  »>, 
—  ^ 

X 

ARRIVAL  CURVES 
on  2500   Mile 
Cable  with 
Terminal 
Condensers 

V 

\ 

X 

L 

\ 

XJ 

^v,^ 

1 

\" 

^ 

\ 

1 

\ 

\ 

\ 

^ 

/ 

S" 

^s 

^ 

\ 

"^ 

// 

X 

s^ 

\ 

1 

^ 

Ss^ 

^ 

^x 

•  —  . 

V 

1 

**  —  . 

~     — 

~     — 

•-       — 

—       , 

— 

0      0.2      0.4     0.6     0.8     1.0 


Seconds 
Fig.  10. 


2.0 


3.0 


By  subtracting  from  curve  II  a  similar  curve  following 
the  first  at  an  interval  of  o.i  second,  the  received  current 
curve  for  a  dot  of  that  duration  will  result,  and  is  shown  in 
Fig,  1 1  by  curve  7.  A  comparison  of  this  curve  with  curve 
T  of  Fig.  4  dispjays  the  fact  that  the  maximum  current  is 
attained  sooner  with  condensers  than  without  them,  but 
this  maximum  is  very  much  lower;  and  further  that  the 
positive  current  lobe  is  followed  by  a  negative  pulse  when 
using  condensers. 

When  the  letters  BT  are  transmitted  over  this  cable  with 
condensers  of  98.7  microfarads  at  each  end,  the  received 


SUBMARINE   TELEGRAPHY 


367 


current  appears  as  in  Fig.  n,  curve  //,  when  the  time  of  a 
dot  or  a  dash  is  o.  i  second.  The  result  is  more  legible  than 
the  curve  of  Fig.  4  for  the  same  signalling  speed  without 


LETTERS  BT   . 

Received  on  2500 

Mile  Cable  with 

Terminal  Condensers 


120 


0    0.1   0.2   0,3   0.4  0.5  0.6  0.7  0.8  0.9    1.0    1.1   1.2   1.3    1.4   1.5  1.6  1.7  1.8   1.9    2 

Seconds 

Pig.  n. 

condensers,  and,  consequently,  the  speed  with  condensers 
might  be  increased  for  the  same  degree  of  legibility.  The 
use  of  condensers  at  the  ends  of  cables  also  serves  to  stop 
earth  currents  and  to  facilitate  duplex  cable  operation  (§  7). 

5.  Picard  Method  of  Signalling.  —  In  transmitting 
signals  over  great  distances  through  several  cables  con- 
nected in  series  the  speed  of  signalling  is  very  low,  but  if 
messages  are  repeated  at  intermediate  stations  the  speed 
of  signalling  is  higher  and  is  limited  by  the  speed  on  that 


368  TELEGRAPH  ENGINEERING 

cable  section  having  the  largest  value  of  CRl2.  This  re- 
peating of  messages  has  been  done  manually,  but  from  time 
to  time  schemes  have  been  devised  and  placed  in  operation 
to  utilize  automatic  retransmission  in  order  to  avoid  error 
and  loss  of  time.  When  the  received  signals  are  such  that 
if  a  straight  zero  line  of  some  width  be  drawn  on  the  tape 
all  of  the  lobes  which  correspond  to  dots  or  dashes  still 
project  on  their  respective  sides  of  this  zero  line,  then  the 
retransmission  of  these  signals  may  be  accomplished  auto- 
matically by  the  use  of  suitable  relays,  such  as  the  Brown 
drum  relay  or  the  Muirhead  gold-wire  relay. 

The  signalling  systems  of  Picard  and  Gott,  using  modi- 
fications of  the  ordinary  Morse  code,  are  arrangements  for 
permitting  the  automatic  retransmission  of  messages,  even 
on  cables  having  a  large  value  of  CRl2. 

In  the  Picard  method,  the  signals  are  formed  by  the  time 
interval  between  two  momentary  oppositely-directed  equal 
impulses,  a  dash  being  distinguished  from  a  dot  by  a  longer 
interval  between  these  impulses.  Thus,  the  impressed 

I     I  I  I    J 


Fig.  12. 

impulses  for  the  letters  BT  are  roughly  shown  in  Fig.  12. 
These  impulses  are  impressed  upon  the  cable  by  means  of 
two  polarized  relays  P,  P'  and  a  local  condenser  C,  con- 
nected as  shown  in  Fig.  13.  A  depression  of  the  key  K 
causes  a  momentary  kick  of  the  right-hand  relay  armature 
against  its  contact  stud  and  connects  the  positive  pole  of 
the  main  battery  B  to  the  cable  for  an  instant.  When  the 


SUBMARINE  TELEGRAPHY 


369 


key  comes  to  rest  after  each  dot  or  dash  signal  the  other 
relay  armature  shifts  and  causes  the  negative  pole  of  the 
battery  to  be  connected  momentarily  to  the  cable.  Be- 
tween these  cable  impulses  the  sending  end  of  the  cable  is 
open-circuited,  and  the  impressed  charge  passes  through 


Cable 


Fig.  13. 

the  receiver.  The  receiving  device  is  a  suspended-coil 
relay  which  has  no  retractile  springs  and  is  free  to  respond 
to  cable  impulses.  This  system  has  been  used  for  many 
years  on  the  three  Marseilles-Algiers  cables  (560  miles) 
belonging  to  the  French  government  for  Morse  signalling 
and  also  for  Baudot  printing  telegraphy  from  Paris  to 
Algiers  with  automatic  translating  relays  at  Marseilles. 

6.  Gott  Method  of  Signalling.  —  The  method  of  cable 
signalling  devised  by  Gott  utilizes  the  Morse  code  of  short 
applications  of  potential  for  dots  and  longer  applications 
for  dashes,  with  successive  elements  in  opposite  directions, 
and  employing  a  sensitive  relay  at  the  receiver.  Inasmuch  as 
a  relay  of  definite  and  sufficient  sensibility  connected  to  the 
far  end  of  a  long  cable  operated  at  high  speed  in  the  ordinary 
way  (§3)  could  not  properly  automatically  retransmit  unidi- 
rectional impulses  into  another  cable  owing  to  the  spreading 
out  of  the  signals  received  by  it,  the  message  in  the  Gott 


370 


TELEGRAPH  ENGINEERING 


system  consists  of  an  assemblage  of  lobes,  alternately  posi- 
tive and  negative,  one  lobe  for  each  dot  and  one  for  each 
dash,  and  the  latter  distinguished  from  the  former  by  their 
greater  length.  Fig.  14  shows  the  results  obtained  by  using 


280 
240 
200 
160 
120 
80 
|40 

1      ° 
|40 

80 
120 
160 

• 

/ 

f 

\ 

GOTT  SYSTEM 
of  Signalling 
Letters  BT  on 
2500  Mile  Cable 

/~* 

\ 

/ 

/ 

\ 

1 

] 

/ 

\ 

/ 

\ 

/ 

\ 

/ 

\ 

/ 

\ 

/ 

\ 

£ 

/ 

\ 

\ 

/ 

\ 

/ 

/ 

\ 

\ 

/ 

\ 

/ 

^/ 

V 

S 

\ 

1 

II 

i 

3 

—  » 

n 

0    0.1    0.2  0.3  0.4    0.5  0.6  0.7  0.8  0.9   1.0    1.1  1.2    1.3   1.4    1.5  1.6    1.7  1.8  1.9    2 

Seconds 
Fig.  14. 

this  method  over  a  long  cable.  The  upper  line  shows 
the  impressed  voltage  on  the  25oo-mile  cable  previously 
considered  with  terminal  condensers,  for  the  letters  BT, 
having  dashes  three  times  as  long  as  dots;  the  curve  shows 
the  current  form  received  at  the  end  of  this  cable  and 
traversing  the  relay;  and  the  lower  line  shows  the  voltage 
impressed  upon  the  second  cable  by  the  relay,  which  is  as- 
sumed to  respond  to  currents  as  small  as  30  microamperes. 
The  curve  is  constructed  by  the  addition  of  properly  placed 
dot  arrival  curves  of  the  type  shown  by  curve  7  of  Fig.  n, 
and  dash  arrival  curves  obtained  by  adding  two  curves 


SUBMARINE  TELEGRAPHY 


371 


(the  latter  reversed)  of  the  type  shown  by  curve  II  of  Fig. 
10  with  an  interval  of  0.3  second  between  them.  It  will 
be  observed  that  the  second  dot  in  Fig.  14  is  very  short 
while  the  third  dot  is  almost  as  long  as  the  dashes.  This 
distortion  of  signals  may  render  deciphering  difficult,  but 
the  method  can  be  improved  upon  by  giving  each  im- 
pressed letter  its  theoretically  best  shape.  Much  better 
results  are  attained  over  shorter  cable  sections. 

One  arrangement  for  automatically  reversing  the  direc- 
tion of  the  voltage  impressed  upon  the  cable  is  shown  in 


Fig.  15. 

Fig.  15.  The  outer  terminals  of  the  split  battery  B  connect 
with  the  contacts  of  the  polarized  relay  P,  and  the  middle 
tap  is  grounded  through  the  primary  winding  of  trans- 
former T.  The  secondary  winding  of  this  transformer  con- 
nects with  the  coils  of  the  relay.  Depressing  the  key  K 
charges  the  cable  with  a  polarity  depending  upon  whichever 
contact  stud  the  relay  armature  is  touching.  Permitting 
the  key  to  resume  its  normal  position  will  cause  the  cable 
to  be  grounded  at  the  sending  end  after  each  signal. 

The  function  of  the  transformer  is  to  control  the  relay 
armature  so  that  successive  impulses  will  always  be  of 
different  polarity.  Assuming  the  armature  to  rest  against 


372  TELEGRAPH  ENGINEERING 

its  left  contact,  depression  of  the  key  will  cause  a  current 
to  be  produced  in  the  secondary  of  the  transformer  and  in 
the  relay  coils  in  such  direction  as  to  hold  the  armature  to  the 
left  contact,  thereby  securing  firm  contact.  Releasing  the 
key  causes  a  current  of  opposite  polarity  to  flow  through 
the  relay  coils,  consequently  the  armature  will  move  against 
the  opposite  contact  stud  in  readiness  for  the  next  signal. 
For  automatic  retransmission,  from  an  overland  line  to  a 
submarine  cable  or  from  one  cable  to  another,  the  key  may 
be  replaced  readily  by  the  armature  of  a  relay. 

The  receiver  employed  with  this  system  is  a  recorder 
with  a  contact-making  tongue  attached  to  the  moving  coil. 
This  tongue  plays  between  two  contacts,  alternately  touch- 
ing one  and  then  the  other.  These  contacts  are  connected 
together  and  lead  to  a  battery  and  sounder  (or  relay)  and 
back  to  the  tongue,  thus  forming  a  local  circuit  for  the  read- 
ing of  the  received  Morse  dot  and  dash  characters. 

7.  Duplex  Cable  Telegraphy.  —  In  modern  practice 
telegraph  cables  are  generally  duplexed  so  that  messages 
may  be  sent  in  both  directions  simultaneously.  This 
practice  involves  the  use  of  an  artificial  cable  equivalent 
in  capacity  and  resistance  to  the  actual  cable  arranged  at 
each  end  of  the  submarine  cable,  as  shown  in  Fig.  16. 
Artificial  cables  may  be  constructed  in  a  variety  of  ways. 
The  Muirhead  artificial  cable  is  widely  used  and  consists 
of  zigzag  tinfoil  sheets,  connected  in  series,  separated  by 
means  of  paraffined  paper  from  other  sheets  of  tinfoil.  The 
latter  sheets  are  grounded,  or  may  be  grounded  through 
resistances,  while  the  zigzag  sheets  are  so  proportioned  as 
to  have  the  requisite  resistance  and  also  the  proper  capacity 
with  respect  to  the  grounded  sheets. 


SUBMARINE  TELEGRAPHY 


373 


The  real  and  artificial  cables  may  be  considered  as  form- 
ing two  arms  of  a  Wheatstone  bridge,  the  other  arms  being 
formed  by  two  nearly  equal  condensers  C\  and  €2  of  from 
30  to  80  microfarads  capacity  each,  arranged  in  the  so- 


Artificial 
Cable 


Fig.  16. 

called  double  block.  One  of  these  condensers  should  be 
slightly  adjustable  in  capacity  so  that  with  the  variable 
resistance,  r,  an  accurate  balance  may  be  secured.  The 
siphon  recorder,  R,  provided  with  an  adjustable  inductive 
shunt,  5,  is  connected  across  the  bridge,  while  the  reversible 
battery  is  connected  from  r  to  ground  through  the  double 
key  K.  The  function  of  the  inductive  shunt  is  to  make 
up  the  deficiency  in  recorder  inductance  for  maximum 
arrival  current,  so  that,  according  to  the  alternating-current 
transmission  theory  already  mentioned,  the  receiving  circuit 
reactance  neutralizes  the  reactance  component  of  the  cable 
surge-impedance.  Another  arrangement  employs  a  con- 
denser in  series  with  the  recorder  and  shunted  by  a  resist- 
ance, the  inductive  shunt  being  bridged  across  both 
condenser  and  recorder. 

When  balance  is  procured,  depression  of  one  of  the  keys 
establishes  a  current  which  divides  equally  in  the  two  cir- 
cuits, one  through  the  condenser  C\  and  the  cable  and  the 
other  through  the  condenser  Ci  and  the  artificial  cable. 
Hence  the  terminals  a  and  b  of  the  recorder  have  the  same 


374  TELEGRAPH  ENGINEERING 

potential  and,  consequently,  no  current  flows  through  this 
instrument.  Thus,  manipulation  of  the  key  does  not  affect 
the  home  recorder. 

If,  however,  a  current  arrives  at  this  end  of  the  cable, 
part  passes  through  the  recorder  to  ground  jointly  through 
the  artificial  cable  and  condenser  Ci,  while  the  remainder 
passes  through  the  condenser  Ci  directly  to  ground.  Thus 
the  key  at  one  end  controls  the  operation  of  the  recorder  at 
the  other  end  of  the  cable.  In  this  way  signals  may  trav- 
erse the  cable  in  opposite  directions  at  the  same  time 
without  interference.  The  Gott  signalling  method  is  also 
applicable  to  duplex  cable  operation.  Considerable  care 
must  be  exercised  in  adjusting  the  artificial  lines  to  secure 
a  good  balance,  and  such  adjustment  is  always  made  with 
the  distant  end  of  the  cables  open-circuited. 

8.  Sine -wave  Signalling.  —  A  method  of  signalling  on 
cables  was  devised  by  Crehore  and  Squier  which  employs 
a  tape  transmitter  for  impressing  half  sine  waves  of  electro- 
motive force  upon  the  cable  instead  of  the  usual  rectangular 
wave-forms.  The  battery  ordinarily  employed  is,  therefore, 
replaced  in  this  system  by  a  low-frequency  alternator.  The 
tape  has  three  lines  of  holes,  the  upper  for  dots,  the  lower 
for  dashes,  and  the  center  line  of  guide  holes  engages  with 
a  toothed  wheel  driven  by  the  alternator  shaft  so  that  the 
tape  travels  a  definite  distance  for  each  revolution  of  the 
alternator  armature.  The  tape  passes  beneath  two  rollers 
attached  to  levers,  which  close  a  local  circuit  at  their  other 
ends  whenever  perforations  move  under  a  roller.  Two 
relays  in  this  local  circuit  connect  the  alternator  to  the 
cable  in  the  proper  way  and  for  a  proper  time.  The  ap- 
pearance of  the  tape  and  the  corresponding  form  of  the 


SUBMARINE  TELEGRAPHY  375 

impressed  voltage  for  the  letters  cab  are  shown  in  Fig.  17. 
The  mechanical  and  electrical  features  of  the  transmitter 
excel  those  of  the  Wheatstone  automatic  transmitter. 


;  o  o  o      coo 

\oooooooooooooo 

o  o     o  o 


This  system  of  signalling  was  operated  experimentally 
by  its  inventors  over  actual  submarine  cables  and  resulted 
in  a  higher  signalling  speed  than  afforded  with  the  usual 
battery  system  under  like  conditions.  Recently,  Malcolm* 
has  published  the  results  of  his  analytical  investigation  of 
this  sine-wave  system  of  cable  signalling,  in  which  he  con- 
cludes that  (a)  the  received  signals  resulting  from  short 
applications  of  any  symmetrical  electromotive  force  are 
independent  of  the  shape  of  the  voltage  wave  and  dependent 
only  upon  its  mean  value,  and  (b)  the  impressed  sine-wave 
voltage  produces  less  shock  at  the  sending  end  of  the  cable 
than  the  abrupt  battery  wave-shapes.  It  is  not  unreason- 
able to  expect  the  commercial  application  of  this  sine-wave 
signalling  system. 

9.  Design  of  Submarine  Cables.  —  A  submarine  cable 
consists  of  a  copper  conductor  surrounded  by  a  tube  of 
gutta-percha  insulation,  all  of  which  is  protected  by  jute 
coverings  and  by  spirally-laid  metallic  armor.  It  has  been 
pointed  out  that  the  speed  of  signalling  on  such  cables 
(ignoring  terminal  apparatus,  inductance  and  leakance) 
varies  inversely  with  the  product  of  the  conductor  resistance 
and  the  capacity  of  the  conductor  with  respect  to  the  sheath. 

*  The  Electrician,  v.  72,  pp.  14-17,  50-52,  131-134,  245-247. 


376  TELEGRAPH  ENGINEERING 

A  large  conductor  surrounded  by  a  thin  tube  of  insulation 
may  have  the  same  product  of  capacity  and  resistance  as  a 
small  conductor  surrounded  by  a  thick  tube  of  insulation, 
but  the  cost  will  be  different.  To  find  the  sizes  of  conduc- 
tor and  insulation  which  yield  the  minimum  cost  of  cable 
of  given  length  for  a  specified  signalling  speed  (that  is,  for  a 
given  value  of  CR),  the  expression  of  total  cost  in  terms  of 
conductor  diameter  is  differentiated  and  equated  to  zero. 
No  cognizance  will  be  taken  of  the  armor  and  other  pro- 
tecting coverings  as  these  items  do  not  affect  the  electrical 
characteristics  of  the  cable,  but  they  may  be  included  in 
determining  the  economic  cable,  if  desired,  without  altering 
the  method  of  procedure. 

The  weight  of  a  copper  wire  one  mile  long  and  having  a 

cross-section  of  one  circular  mil  is  0.016  pound.     If  c\  be 

the  cost  of  copper  in  dollars  per  pound,  then  the  cost  of  a 

stranded  conductor  /  miles  long  and  D  mils  in  diameter  is 

0.016  sD2ki  dollars,  (14) 

where  s  is  the  stranding  factor  or  the  ratio  of  the  copper 
cross-section  in  circular  mils  to  the  cross-section  of  the 
circle  of  diameter  Z);  thus,  for  a  seven-strand  conductor 
having  strands  of  equal  size,  s  =  ^. 

If  d  be  the  diameter  in  mils  over  the  insulation,  the  vol- 
ume of  insulation  will  be 

12  X  528°/  (d2  -  D2)  =  0.0497 1  (^  -  D2)  cu.  in., 
1,273,240 

where  1,273,240  is  the  number  of  circular  mils  in  a  square 
inch.  Taking  8  as  the  density  of  the  insulating  material 
in  pounds  per  cubic  inch,  and  c2  as  the  cost  in  dollars  per 
pound  of  this  material,  its  cost  will  be 

0.0497  /  (d2  -  D2)  5^2.  (15) 


SUBMARINE  TELEGRAPHY  377 

As  the  capacity  of  two  concentric  cylinders  i  mile  long, 
the  inner  of  diameter  D  and  the  outer  of  diameter  d,  sepa- 
rated by  a  medium  of  uniform  specific  indue  tivity  k,  is 

^      0.0804  k     .      .      j 
C  =  -  ^—  microfarads 


(§  7,  Chap.  IX),  and  as  the  resistance  of  the  stranded  con- 
ductor, having  a  resistivity  of  p  ohms  per  circular-mil  mile 
at  sea  temperature,  is 


it  follows  that  the  product  is 

0.0894  Pk 


K_ 

whence  d  =  DeD*,  (16) 

r. 


Substituting  this  value  of  d  in  equation  (15)  and  com- 
bining with^(i4),  the  total  cost  of  the  cable  exclusive  of 
armor  and  other  coverings  is 

(2K  \ 

c^-l).      (17) 

Differentiating  and  equating  to  zero,  there  results 

/  *K\  .?* 

0.032  sDld  +  0.0497  Ifa  f  2  D  -  ^—  J  e  D*  -  0.0994  /5Z>C2  =  o 

IlK  \     ^         0.03  2  Ci5 

or    ( -rrr-  —  i  j  €  "  =  -  -  —  i  =  /^  for  convenience. 

V  D*         /  0.0994  ^5 


378 


TELEGRAPH   ENGINEERING 


It  is  possible  to  determine  D  from  this  expression  in  terms 
of  the  known  factors  K  and  F,  and  this  is  best  done  graphi- 
cally. Fig.  1 8  shows  the  relation  of  -=— -  to  F. 


1.4 

1.3 
1.2 

1.1 

D2" 
0.9 

0.8 

0.7 
0.6 
0.5 

-: 

^ 

^ 

/ 

/ 

^ 

/ 

7 

/ 

/ 

7- 

-0.8     -0.6    -0.4     -0.2         0         0.2       0.4       0.6       0.8       l.O       1.2       1. 

Fig.  18. 

As  a  numerical  illustration,  let  it  be  required  to  design 
the  most  economical  25oo-mile  seven-strand  submarine 
cable  for  a  value  of  CR  =  0.6  ohm-mf.  per  mile  (that  is 
CR/2  =  3.75  seconds).  Let 

Ci  =  0.16 
c2  =  0.80 
6  =  0.037 
k  =  3.04 
p  =  51,000, 

then        F  =  0.032X0.16X0.778 
0.0994  X  0.80  X  0.037 


SUBMARINE  TELEGRAPHY  379 


and          g  =  o.o894  X  ,V°4  X  5          = 
0.6  X  0.778 

From  Fig.  18,  for  F  =  0.354,  —  =  1.115  and,  therefore,  the 
diameter  of  the  stranded  conductor  is 


~  /20,7OO  X  2  ., 

D  =  \     V;/          -  =  231  mils, 
V      i. nc 


and  the  diameter  over  insulation  is 

29,700* 

d  =  231  e(231)1  =  403  mils. 

The  total  cost  of  the  conductor  and  insulating  material 
as  determined  from  equation  (17)  is  265,000  +  401,000  = 
666,000  dollars. 

Had  the  conductor  been  a  single  wire  (i.e.,  5  =  i)  the 
cost  would  be  less  for  the  same  signalling  speed.  Its  diam- 
eter would  then  have  been  196  mils  and  its  diameter  over 
insulation  358  mils  (no  correction  being  made  for  increase 
in  resistance  due  to  stranding) .  The  cost  would  be  $5 76,000. 
Solid  conductors,  however,  are  not  frequently  used  because 
of  the  greater  liability  of  fracture  in  laying  the  cable. 

To  make  certain  that  the  stranded  cable  has  sufficient 
insulation   resistance,    the   foregoing   diameters   are   sub- 
stituted in  the  following  equation: 
'  i 

Insulation  resistance  =  —  I    —  =  —  loge—      (18) 
2  irJo  x       2  TT        D 

2 

megohms  per  mile,  where  a  is  the  resistance  in  megohms 

between  opposite  faces  of  a  cube  of  the  insulation  one  mile 

on  a  side  when  at  sea  temperature  but  at  atmospheric 

*  See  Table  of  Exponential  Functions  in  Appendix. 


380  TELEGRAPH  ENGINEERING 

pressure.  Taking  o-  =  28,000  in  the  numerical  illustration, 
the  insulation  resistance  will  be  2480  megohms  per  mile. 
Under  the  enormous  pressures  existing  at  great  depths  under 
water,  the  insulation  resistance  of  the  cable  when  laid  is 
greater  than  when  tested  in  the  factory.  Taking  0.05  per 
cent  increase  per  fathom  (i  fathom  =  6  feet)  the  insula- 
tion resistance  at  a  depth  of  1500  fathoms  will  be  4340 
megohms  per  mile,  which  is  adequate.  The  design  of 
cables  for  specified  insulation  resistance  is  of  secondary 
importance  to  signalling  speed,  inasmuch  as  leakance  rel- 
atively affects  the  shape  or  amplitude  of  the  arrival  current 
curve  but  little,  so  long  as  it  remains  constant. 
The  weight  of  conductor  and  insulation  is 


0.016  sD2  +  0.0497  (<P  ~  D2)*  <. 

^^  -  —  tons  per  mile, 
2000 

which  weight  is  generally  less  than  one-fifth  of  the  total 
weight  of  the  cable.  The  amount  of  protection  on  cables 

depends  on  the  depth  of  sub- 
mergence,  and  is  light  on  deep- 
&  compound  sea  cable  sections  and  heavy 
°~7  stconductor  ^or  ^ne  shore-end  sections  of 
-jute  Yam  cables.  In  order  to  facilitate 
the  k^  and  ^covering  of 
cables  they  should  be  as  light 
as  is  consistent  with  the  stresses 

to  which  they  are  subjected.  Weights  of  galvanized  iron 
or  steel  cable  sheaths  for  various  depths  of  cable  sub- 
mergence are  indicated  roughly  by 

-  -  r^  —  ;  -  ^rz  tons  per  mile. 
(depth  in  fathoms)0'8 


SUBMARINE  TELEGRAPHY 


381 


The  weight  of  jute,  tape  and  preservative  compound  may 
be  from  40  to  100  per  cent  of  the  weight  of  the  metallic 
sheath.  Fig.  19  shows  to  proper  size  the  cross-section  of 
the  25oo-mile  cable  considered  in  this  article,  well  pro- 
tected for  a  depth  of  1500  fathoms. 

The  electrical  constants  of  a  few  long  cables  are  given 
below : 


Cable 

Length  in 
miles* 

Total  re- 
sistance in 
ohms 

Total  ca- 
pacity in 
microfarads 

Anglo-American   Atlantic   (Valentia 
to  Heart's  Content)      .    .  . 

2I2O 

7,288 

776 

Second  German  Atlantic  (Borkum  to 
Fayal)  

22O7 

^218 

Pacific  (Fanning  Island  to  Fiji).  .  .  . 
Atlantic  (Canso  to  Waterville)  
Commercial  Pacific  (San  Francisco 
to  Honolulu) 

2354 
2493 

2622 

10936 
4895 

4O7  ^ 

746 
914 

87< 

*  Distances  over  sea  are  more  frequently  expressed  in  nautical  miles  (nauts);  i  naut  = 
1.152  miles. 

The  cost  of  laying  a  cable  is  generally  estimated  as  half 
of  the  cost  of  the  cable.  The  life  of  a  submarine  cable  is 
variously  estimated  as  from  30  to  40  years;  in  fact,  por- 
tions of  cables  laid  from  1851  to  1854  from  England  to 
neighboring  countries  are  still  in  use. 

The  commercial  status  of  submarine  telegraphy  is  indi- 
cated by  the  fact  that  in  1911  there  were  over  2000  cables 
in  the  world  aggregating  314,000  miles  of  cable  and  repre- 
senting an  estimated  investment  of  350  million  dollars. 

10.  Types  of  Cable  Service  and  Tariffs.  —  There  are 
two  types  of  cable  service  rendered  at  present  by  some  of 
the  large  telegraph  companies,  namely:  full-rate  service  for 
code  and  urgent  messages  requiring  prompt  transmission 
and  delivery,  and  deferred  service  to  many  countries  for 


382  TELEGRAPH  ENGINEERING 

messages  in  plain  language  not  requiring  the  greatest  ex- 
pedition and  involving  transmission  within  24  hours.  In 
addition  the  Western  Union  Telegraph  Company  renders 
cable  letter  service  and  week-end  letter  service  across  the  At- 
lantic for  less  important  communications  in  plain  language 
which  should  not  be  subjected  to  the  delay  of  over-sea 
mails.  The  following  conditions  and  rates  apply  at  present 
(July,  1914)  to  the  various  types  of  service. 

All  Classes.  Addresses  and  signatures  are  counted  and 
charged  for,  but  no  charge  is  made  for  name  of  originating 
city  and  date.  In  addresses,  the  names  of  delivery  offices, 
countries,  provinces,  states,  etc.,  are  each  counted  as  one 
word  regardless  of  the  number  of  letters  employed.  The 
cost  of  full  addresses  may  be  avoided  by  using  code  ad- 
dresses, which  are  permitted  by  all  governmental  adminis- 
trations upon  payment  of  a  fee.  In  plain  language,  words 
of  15  letters  or  less  are  counted  as  one  word.  Abbreviated 
words  and  illegitimate  combinations  of  words  are  inadmis- 
sible. Every  isolated  character  counts  as  one  word,  and 
words  joined  by  a  hyphen  or  separated  by  an  apostrophe 
are  counted  as  separate  words.  Punctuation  marks  are 
only  transmitted  upon  the  expressed  desire  of  the  sender, 
and  then  charged  for  as  one  word  each. 

Full-rate  service.  Full-rate  messages  may  be  in  code  or 
cipher  language  or  in  any  plain  language  expressible  in 
Roman  letters.  Code  messages,  formed  of  regular  or  arti- 
ficial words  not  making  intelligible  phrases,  must  be  pro- 
nounceable and  must  not  contain  more  than  10  letters. 
Cipher  messages,  formed  of  either  unpronounceable  groups 
of  letters  or  of  groups  of  figures,  are  counted  at  the  rate  of 
5  characters,  or  fraction  thereof,  to  a  word.  The  presence 
of  a  code  word  in  an  otherwise  plain  language  message 


SUBMARINE  TELEGRAPHY 


383 


subjects  the  entire  message  to  the  lo-letter  code  count,  but 
plain  language  words  in  cipher  messages  are  reckoned  15 
letters  to  a  word.  If  unpronounceable  groups  of  letters 
appear  in  code  or  plain  language  messages,  such  groups  are 
subject  to  the  5-letter  cipher  count.  Fraction  bars,  periods, 
commas  and  decimal  points  grouped  with  figures  count  as 
figures.  Replies  to  a  message  may  be  prepaid  by  writing 
before  the  name  and  address  the  letters  RP  followed  by  the 
figure  showing  the  number  of  words  prepaid  (this  indica- 
tion is  charged  as  one  word).  The  following  table  shows 
the  rates  per  word  to  points  in  some  of  the  principal  coun- 
tries from  New  York  City. 

Present  cable  rates  in  cents  (July,  1914) 


'Argentine  Republic 

65 

'Australia 

66 

'Austria-Hungary 

32 

'Belgium    

25 

Bermuda  

42 

61 

'Brazil     '.  

70-249 

Bulgaria!  

35 

AC 

'Cape  Colony  
'Chili  

86 
65 

Philippine  Islands  
Porto  Rico  

112-136 

JChina  (except  Macao  =127)  

122 

'Portugal  

Cuba  (except  Havana  =15)  

2O 

Roumaniaf.  .  .                       

'Denmark 

•ir 

'Egypt  

50-58 

'Serviaf 

43 

'France  

25 

Siam 

'Germany  

25 

'Spain 

'Great  Britain  and  Ireland  

25 

'Sweden  

38 

'Greece  

36 

'Switzerland 

'Holland  

25 

'Transvaal 

86 

Honduras  

55 

Turkey  (in  Europe)f 

'India  

74 

'Uruguay 

6< 

•Italy  

31 

Venezuela 

*  Countries  to  which  Deferred  Service  may  be  utilized  at  present, 
f  Secret  language  prohibited. 

J  Deferred  service  only  to  Pekin,  Hankow,  Tientsin,  Amoy,  Chefoo,  Foochow,  Shang- 
hai, Tsingtau,  Weihaiwei,  Hong  Kong,  and  Macao. 

It  is  of  historical  interest  to  recall  that  in  the  early  pioneer  days  of  transatlantic  te- 
legraphy the  minimum  tariff  was  £20  ($100)  for  20  words  and  £i  for  each  additional  word. 


384  TELEGRAPH  ENGINEERING 

Deferred  service.  Deferred  messages  must  be  written  in 
one  language  which  may  be  that  of  the  country  of  origin 
or  of  destination  or  may  be  in  French,  the  letters  LCO, 
LCD  or  LCF  respectively  being  prefixed  to  the  address  as 
indicative  of  the  type  of  service  and  the  language  used 
(one  word  is  charged  for  this  indication  or  prefix).  The 
text  of  the  message  must  be  entirely  in  plain  language, 
numbers,  except  in  addresses,  being  also  written  in  words. 
The  rates  for  deferred  service  is  one-half  those  shown  in 
the  foregoing  table  to  the  countries  therein  starred,  except 
to  Great  Britain  and  Ireland  where  the  rate  is  9  cents  per 
word.  Replies  may  be  prepaid  as  in  full-rate  service  but 
the  instruction  as  to  the  number  of  words  prepaid  must  be 
expressed  in  terms  of  full  rates. 

Cable  and  Week-end  letter  service.  Cable  and  week-end 
letters  must  be  written  in  plain  language  of  the  country  of 
origin  or  of  destination,  the  indication  CLP  or  CLT  and 
WLP  or  WLT  respectively  being  prefixed  to  the  address  as 
indicative  of  the  type  of  service  and  the  method  of  delivery 
beyond  London  or  Liverpool,  whether  by  post  or  telegraph. 
Cable  letter  tolls  are  based  on  an  initial  charge  of  75  cents 
for  12  words  (13  including  indication)  and  week-end  letters 
on  an  initial  charge  of  $1.15  for  24  words  (25  including 
indication),  plus  5  cents  for  each  additional  word  in  both 
cases.  These  charges  cover  cable  transmission  only  and  do 
not  include  terminal  telegraphic  charges.  The  letters  may 
be  mailed  to  the  New  York  Western  Union  Cable  Office,  the 
week-end  letters  being  sent  in  time  for  mail  delivery  at  this 
office  on  Saturday  evenings.  The  charges  cover  delivery 
in  London  or  Liverpool  and  mail  delivery  to  all  other  places 
abroad.  With  telegraphic  delivery  beyond  these  cities  cable 
letters  are  deliverable  during  the  day  following  their  date 


SUBMARINE   TELEGRAPHY  385 

and  week-end  letters  on  Monday  forenoon ;  and  the  follow- 
ing additional  charge  per  word  is  made  to  points  in :  Great 
Britain  and  Ireland  —  i  cent,  Holland  and  Belgium  —  2 
cents,  France— yi  cents,  Italy—  6  cents,  Germany— 9  cents, 
and  in  other  countries  at  the  regular  foreign  rates.  Figures 
when  not  used  as  cipher  are  counted  each  group  of  5  or  less 
as  a  word.  Replies  may  be  prepaid  as  in  deferred  service. 
Cable  letter  service  is  likewise  in  operation  with  Cuba, 
the  rate  between  New  York  and  Havana  being  one  dollar 
for  20  words  (including  prefix),  plus  5  cents  for  each  addi- 
tional word.  Double  this  rate  applies  to  letters  for  other 
points  in  Cuba.  Week-end  letter  service  is  in  operation 
with  Argentine  Republic,  Chili  and  Peru,  and  the  tariff 
between  New  York  and  these  countries  is  $4.85  for  24 
words  (25  including  prefix)  plus  20  cents  for  each  additional 
word,  the  letters  being  delivered  on  Tuesday  mornings. 

PROBLEMS 

1.  Compute  the  values  of  the  current  received  at  one  end  of  the 
2129-mile  Anglo-American  Atlantic  cable,  having  R  =  1.591  ohms 
per  mile  and  C  =  0.3645  microfarad  per  mile,  at  instants  respectively 
of  0.2,  0.4,  0.6,  0.8,  i.o,  1.4,  1.8,  and  2.5  seconds  after  impressing  30 
volts  on  the  cable;   also  plot  a  curve  showing  these  values  co-ordi- 
nated to  time. 

2.  From  the  curve  of  the  preceding  problem  construct  graphically 
the  curve  of  arrival  on  this  Atlantic  cable  of  a  dot  element  for  a  con- 
tact on  30  volts  lasting  0.05  second. 

3.  Using  the  dot  arrival  curve  of  the  foregoing  problem  as  a 
basis,  construct  the  shape  of  signals  received  over  the  cable  for  any 
three-letter  word. 

4.  What  may  be  the  signalling  speed  in  terms  of  5 -letter  code 
words  on  a  icoo-mile  cable  having  a  total  resistance  of  3000  ohms  and 
a  total  capacity  of  350  microfarads  for  the  same  legibility  of  received 
signals  as  represented  by  Fig.  4. 


386  TELEGRAPH  ENGINEERING 

5.  Plot  the  received  signals  for  the  letters  HE  (for  T  =  o.i  second 
with  40  volts)  sent^through  the  25oo-mile  cable  considered  in  §§  2  to 
4  according  to  the  Gott  system.     Curve  I  of  Fig.  n  shows  the 
magnitude  and  shape  of  the  dot  element.     Show  the  type  of  signals 
retransmitted  into  another  cable  if  the  receiving  relay  is  actuated  by 
a  current  of  40  microamperes. 

6.  Determine  the  economic  dimensions  of  the  conductor  and 
insulation  of  the  cable  considered  in  §  9  if  the  cost  of  insulation  be 
taken  as  55  cents  per  pound,  other  constants  remaining  unaltered. 

7.  Calculate  the  weights  per  mile  and  the  total  cost  of  7-strand 
conductor  and  insulation  for  a  looo-mile  cable  having  a  value  of 
CR  =  1.05  X  io~6  seconds.    The  cost  of  copper  is  17  cents  and  the 
cost  of  insulation  is  i  dollar  per  pound.    Take  k  =  3.1. 

8.  What  would  be  the  possible  maximum  annual  net  income  of  a 
duplexed  cable  when  continuously  used  for  automatic  transmission 
of  code  messages  averaging  8.5  letters  to  the  word  and  9  words  to  the 
message,  if  the  dot  element  T  is  0.05  second  and  the  space  between 
messages  is  12  T  (the  symbol  "  understand"— 3  dots,  dash,  dot,  is 
frequently  used  between  messages);  the  apportioned  revenue  over 
this  cable  section  being  8  cents  per  word  ?    Two  operators  prepare 
tapes  and  feed  the  transmitter  and  two  decipher  the  received  mes- 
sages; they  work  in  8  hour  shifts  and  receive  an  average  weekly 
salary  of  26  dollars.     Allow  3  per  cent  depreciation  on  the  cost  of 
the  cable  installed  and  terminal  apparatus,  which  was  $1,000,000. 

9.  How  much  would  it  cost  to  send  the  following  cable  letter: 

CLT-RP  10  Instrument  Cambridge 

Give  price  and  delivery  spectrophotometer  and  radio-micrometer 
with  scale  Richardbrown  Brooklyn. 

10.  Decipher  the  message  reproduced  below  which  was  received 
over  a  i6oo-mile  cable. 


nf-AT^AAAM 


f\A  /VA/^V^ 


APPENDIX 

TABLES   OF  TRIGONOMETRIC  FUNCTIONS, 

EXPONENTIAL  FUNCTIONS,  LOGARITHMS  AND 

HYPERBOLIC  FUNCTIONS 


387 


388 


TELEGRAPH  ENGINEERING 


TABLE  I.  —  TRIGONOMETRIC   (CIRCULAR)  FUNCTIONS 


H 

u 

Degrees 

Radians 

Degrees 

Radians 

0 

o 

o 

I  OOOO 

13.5 

o  2334 

o  9724 

o  5 

o  0087 

I  OOOO 

o  24 

2377 

9713 

O.OI 

OIOO 

0.9999 

14.0- 

2419 

97O3 

I  O 

0175 

0008 

0680 

1-5 

02 

O20O 
O262 

9998 

9997 

14-5 

26 

2504 
2571 

9681 
9664 

03 

O3OO 

9996 

15.0 

2588 

9659 

2.O 

O349 

9994 

27 

2667 

9638 

04 

O4OO 

9992 

15.5 

2672 

9636 

2.5 

0436 

9990 

16.0 

2756 

9613 

0088 

28 

96ll 

3-0 
3-5 

06' 

0523 
O6OO 
o6lO 

9986 
9982 
9981 

16.5 

17  o 

29 

2840 
2860 
2924 

9588 
9582 
9563 

4.0 

0698 

9976 

30 

2955 

9553 

07 

0699 

9976 

17.5 

3007 

9537 

4.5 

0785 

9969 

3i 

3051 

9523 

08 

0068 

.  S.o 

0872 

9962 

32 

3146 

9492 

09 

0899 

9960 

18  5 

3173 

9483 

5-5 

0958 

9954 

33 

3240 

9460 

6.0 

IO45 

9945 

34 

3335 

9428 

ii 

1098 

\r*8 

9426 

6.5 

1132 

9936 

20  o 

3420 

9397 

7.0 

12 

"97 
1219 

9928 
9925 

20  5 

35 

3429 
3502 

9394 
9367 

13 

o(j 

1C2"* 

9359 

7-5 

1305 

9914 

21  O 

3584 

9336 

8.0 

1392 

9903 

37 

36l6 

9323 

14 

1395 

9902 

21  5 

3665 

9304 

8.5 

1478 

9890 

38 

37O9 

9287 

It; 

9888 

9-0 

1564 

9877 

39 

3302 

9249 

16 

IITQ-I 

0872 

•7827 

9239 

9-5 

l65O 

9863 

40 

3894 

9211 

17 

1692 

9856 

23.O 

3907 

9205 

10.  0 

1736 

9848 

41 

3986 

9171 

18 

I79O 

9838 

23  5 

3987 

9171 

10.5 

1822 

9833 

24  o 

4067 

9135 

II.  0 

II.  5 

19 

20 

1889 
1908 
1987 
1994 

9820 
9816 
9801 
9799 

24-5 
25  o 

42 
43 

4078 
4147 
4169 
4226 

9131 

9100 
9090 
9063 

12.0 

2O79 

9781 

9048 

12.5 

21 

2085 
2164 

9780 

25.5 

4305 

9026 

13.0 

22 

2182 

9759 

26.0 

^6 

4384 

8988 
8961 

» 

23 

2280 

9737 

26.5 

4462 

8949 

APPENDIX 


389 


TABLE  I.  — TRIGONOMETRIC   (CIRCULAR)  FUNCTIONS—  (Continued) 


u 

U 

Degrees 

Radians 

Degrees 

Radians 

27  o 

0.47 

0.4529 
4540 

0.8916 
8910 

37-5 

o  66 

0.6088 
6131 

0.7934 
7900 

27-S 
28  o 

'"48" 

4617 
4618 
4695 

8870 
8870 
8829 

38.0 
38  5 

67 

6i57 
6210 
6225 

7880 
7838 
7826 

49 

4706 

8823 

68 

6288 

7776 

28.5 
29.0 

50 
51 

4772 
4794 
4848 
4882 

8788 
8776 
8746 
8727 

39-0 
39-5 

40.0 

'"69" 

6293 
6361 
6365 
6428 

7771 
7716 
7713 
7660 

29.5 

4924 

8704 

70 

6442 

7648 

30  o 

52 

4969 
5000 

8678 
8660 

40.5 

71 

6494 
6518 

7604 
7584 

53 

5055 

8628 

41  o 

6561 

7547 

30.5 

31.0 

54 

5075 
5141 
5150 

8616 
8577 
8572 

41-5 

72 
73 

6594 
6626 
6669 

75i8 
7490 
7452 

31  5 

5225 

8526 

42  o 

6691 

7431 

55 

5227 

8525 

74 

6743 

7385 

32.0 
32.5 

56 

5299 

5312 

5373 

8480 

8473 
8434 

42.5 

43  o 

75 

6756 

6816 
6820 

7373 

7317 
7314 

57 

5396 

8419 

43  5 

6884 

7254 

33.0 

5446 

8387 

76 

6889 

7248 

33.5 

58 

548o 
5519 

836S 
8339 

44.0 

77 

6947 
6961 

7193 
7179 

59 

5564 

8309 

44  5 

7009 

7133 

34.0 

5592 

8290 

78 

7033 

7109 

60 

5646 

8253 

45.O 

7071 

7071 

34-5 

5664 

8241 

79 

7104 

7O39 

35-0 
35-  5 

36.0. 
36.5 
37-0 

61 

62 
'"63" 
64 
'  6s" 

5729 
5736 
5807 
5810 
5878 
5891 
5948 
5972 
6018 
6052 

8197 
8192 
8141 
8i39 
8090 
8080 
8039 
8021 
7986 
796l 



80 
85 
90 
.00 
.10 
.20 
•  30 
.40 
•  50 
.60 

7174 
7513 
7833 
8415 
8912 
9320 
9636 
9855 
9975 
9996 

6967 
6600 
6216 
5403 
4536 
3624 
2675 
1700 
0707 
—  .0292 

The  functions  of  larger  angles  are: 


Function 

When  angle  u  lies  between 

45°  and  90° 

90°  and  180° 

180°  and  270° 

270°  and  360° 

sin  u  = 
cos  «= 

cos  (90°  —  M) 
sin  (90°  —  «) 

sin  (180°  —  u) 
—  cos  (180°  —  M) 

—  cos  (270°  —  u) 
—  sin  (270°  —  «) 

—  sin  (360°  —  u) 
cos  (360°  —  M) 

390 


TELEGRAPH  ENGINEERING 


TABLE   II.  —  EXPONENTIAL  FUNCTIONS 


« 

e* 

e-u 

u 

e" 

•-* 

u 

« 

r" 

0 

I.  0000 

I.  0000 

0.50 

1.6487 

0.6065 

I.OO 

2.7183 

0.3679 

0.01 

OIOI 

0.9901 

51 

6653 

6005 

02 

7732 

3600 

02 

O2O2 

9802 

52 

6820 

5945 

04 

8292 

3535 

03 

0305 

9704 

S3 

6989 

5886 

06 

8864 

3465 

04 

0408 

9608 

54 

7160 

5827 

08 

9447 

3396 

OS 

0513 

9512 

55 

7333 

5769 

10 

3.0042 

3329 

06 

O6l8 

9418 

56 

7507 

5712 

12 

0649 

3263 

07 

0725 

9324 

57 

7683 

5655 

14 

1268 

3198 

08 

0833 

9231 

58 

7860 

5599 

16 

1899 

3135 

09 

0942 

9139 

59 

8040 

5543 

18 

2544 

3073 

10 

1052 

9048 

60 

8221 

5488 

20 

3201 

3012 

II 

Il63 

8958 

6l 

8404 

5434 

22 

3872 

2952 

12 

1275 

8869 

62 

8589 

5379 

24 

4556 

2894 

13 

1388 

8781 

63 

8776 

5326 

26 

5254 

2837 

14 

1503 

8694 

64 

8965 

5273 

28 

5966 

2780 

IS 

1618 

8607 

65 

9155 

5220 

30 

6693 

2725 

16 

1735 

8521 

66 

9348 

5169 

32 

7434 

2671 

17 

1853 

8437 

67 

9542 

5117 

34 

8190 

2618 

18 

1972 

8353 

68 

9739 

5066 

36 

8962 

2567 

19 

2093 

8270 

69 

9937 

5016 

38 

9749 

2516 

20 

2214 

8187 

70 

2.0137 

4966 

40 

4.0552 

2466 

21 

2337 

8106 

71 

0340 

4916 

42 

1371 

2417 

22 

2461 

8025 

72 

0544 

4868 

44 

2207 

2369 

23 

2586 

7945 

73 

0751 

4819 

46 

3060 

2322 

24 

2712 

7866 

74 

0959 

4771 

48 

3929 

2276 

25 

2840 

7788 

75 

1170 

4724 

50 

4817 

2231 

26 

2969 

7711 

76 

1383 

4677 

52 

5722 

2187 

27 

3100 

7634 

77 

1598 

4630 

54 

6646 

2144 

28 

3231 

7558 

78 

1815 

4584 

56 

7588 

2101 

29 

3364 

7483 

79 

2034 

4538 

58 

8550 

8000 

30 

3499 

7408 

80 

2255 

4493 

60 

9530 

2019 

31 

3634 

7334 

81 

2479 

4449 

62 

5.0531 

1979 

32 

3771 

7261 

82 

2705 

4404 

64 

1552 

1940 

33 

3910 

7189 

83 

2933 

436o 

66 

2593 

1901 

34 

4049 

7118 

84 

3164 

4317 

68 

3656 

1864 

35 

4191 

7047 

85 

3396 

4274 

70 

4739 

1827 

36 

4333 

6977 

86 

3632 

4232 

72 

S84S 

1791 

37 

4477 

6907 

87 

3869 

4190 

74 

6973 

1755 

38 

4623 

6839 

88 

4109 

4148 

76 

8124 

1720 

39 

4770 

6771 

89 

4351 

4107 

78 

9299 

1686 

40 

4918 

6703 

90 

4596 

4066 

80 

6.0496 

1653 

41 

5068 

6637 

91 

4843 

4025 

82 

1719 

1620 

42 

5220 

6570 

92 

5093 

3985 

84 

2965 

1588 

43 

5373 

6505 

93 

5345 

3946 

86 

4237 

1557 

44 

5527 

6440 

94 

5600 

3906 

88 

5535 

1526 

45 

5683 

6376 

95 

5857 

3867 

90 

6859 

1496 

46 

5841 

6313 

96 

6117 

3829 

92 

8210 

1466 

47 

6000 

6250 

97 

6379 

3791 

94 

9588 

1437 

48 

6161 

6188 

98 

6645 

3753 

96 

7.0993 

1409 

49 

6323 

6126 

99 

6912 

37i6 

98 

2427 

1381 

APPENDIX 


391 


TABLE  II.  —  EXPONENTIAL  FUNCTIONS  —  (Continued) 


u 

t« 

_u 

€ 

u 

t« 

*-" 

2.OO 

7.3891 

0.13534 

4-50 

00.017 

O.OIIIOO 

05 

7679 

12873 

55 

94.632 

010567 

10 

8.1662 

12246 

60 

99.484 

010052 

IS 

5849 

11648 

65 

104.585 

009562 

20 

9  .  0250 

11080 

70 

109.947 

009095 

25 

4877 

10540 

75 

H5.584 

008652 

30 

9742 

10026 

80 

I2I.5IO 

008230 

35 

10.4856 

09537 

85 

127.740 

007828 

40 

11.0232 

09072 

90 

134-290 

007447 

45- 

11.5883 

08629 

95 

I4LI75 

007083 

50 

12.1825 

08209 

S.oo 

I48.4U 

006738 

55 

12.8071 

07808 

05 

156.022 

006409 

60 

13.4637 

07427 

10 

164.022 

006097 

65 

14.1540 

07065 

IS 

172.431 

005799 

70 

14.8797 

06721 

20 

181  .  272 

005517 

75 

15.6426 

06393 

25 

190.566 

005248 

80 

16.4446 

06081 

30 

200.337 

004992 

85 

17-2878 

05784 

35 

210.608 

004748 

90 

18.1741 

05502 

40 

221  .  406 

004517 

95 

19.1060 

05234 

45 

232.758 

004296 

3.00 

20.086 

04979 

50 

244.692 

004087 

05 

21.115 

04736 

55 

257.238 

003888 

10 

22.198 

0450S 

60 

270.426 

003698 

15 

23.336 

04285 

65 

284.291 

003518 

20 

24-533 

04076 

70 

208.867 

003346 

25 

25.790 

03877 

75 

3I4.I9I 

003183 

30 

27.113 

03688 

80 

330.300 

003028 

35 

28.503 

03508 

85 

347-234 

002880 

40 

29.964 

03337 

90 

365.037 

002739 

45 

31.500 

03175 

95 

383.753 

002606 

50 

33-115 

03020 

6.00 

403.43 

0024788 

55 

34.813 

02872 

7.00 

1,006.6 

0009119 

60 

36.598 

02732 

8.00 

2,98l.O 

00033546 

65 

38.475 

02599 

9.00 

8,103.1 

00012341 

70 

40.447 

02472 

10.00 

22,026 

000045400 

75 

42.521 

02352 

11.00 

59,874 

000016702 

80 

44-701 

02237 

12.  OO 

162,754 

000006144 

85 

46-993 

02128 

13.00 

442,413 

0000022603 

90 

49-402 

02024 

14.00 

1,202,600 

00000083153 

95 

51-935 

01925 

15.00 

3,269,000 

00000030590 

4.00 

54.598 

01832 

16.00 

'  8,886,100 

00000011253 

05 

57-397 

01742 

17.00 

24,155,000 

000000041399 

10 

60.340 

01657 

18.00 

65,660,000 

000000015230 

IS 

63.434 

01576 

19.00 

178,482,000 

0000000056028 

20 

66.686 

01500 

20.00 

485,165,000 

0000000020612 

25 

70.105 

01426 

21.00 

1,318,800,000 

00000000075826 

30 

73-700 

OI3S7 

22.00 

3,584,000,000 

00000000027895 

35 

77.478 

01291 

23.00 

9,744,800,000 

00000000010262 

40 

81.451 

01228 

24.OO 

26,489,100,000 

00000000003775 

45 

85.627 

01168 

25.00 

72,004,800,000 

00000000001389 

392 


TELEGRAPH  ENGINEERING 


TABLE  III.  —  LOGARITHMS  TO  BASE  10 


No. 

0 

I 

2 

3 

4 

5 

6 

7 

8 

9 

10 

00000 

00432 

00860 

01284 

01703 

02119 

02530 

02938 

03342 

03743 

ii 

04139 

04532 

04922 

05307 

05690 

06070 

06446 

06819 

07188 

07555 

12 

07918 

08279 

08637 

08990 

09342 

09691 

10037 

10380 

10721 

11059 

13 

1  1394 

11727 

12057 

12385 

12710 

13033 

13354 

13672 

13988 

14301 

14 

14613 

14922 

15229 

15533 

15836 

16137 

16435 

16732 

17026 

I73I9 

IS 

17609 

17898 

18184 

18469 

18752 

19033 

I93I2 

19590 

19866 

20140 

16 

20412 

20683 

20952 

21219 

21484 

21748 

2201  1 

22272 

22531 

22789 

17 

23045 

23300 

23553 

23805 

24055 

24304 

24551 

24797 

25042 

25285 

18 

25527 

25768 

26007 

26245 

26482 

26717 

26951 

27184 

27416 

27646 

19 

27875 

28103 

28330 

28556 

28780 

29003 

29226 

29447 

29667 

29885 

20 

30103 

30320 

30535 

30749 

30963 

3H75 

31386 

31597 

31806 

32015 

21 

32222 

32428 

32633 

32838 

33041 

33244 

33445 

33646 

33846 

34044 

22 

34242 

34439 

34635 

34830 

35025 

352i8 

3541  1 

35603 

35793 

35984 

23 

36173 

36361 

36549 

36736 

36922 

37107 

37291 

37475 

37658 

37840 

24 

38021 

38202 

38382 

38561 

38739 

38916 

39094 

39270 

39445 

396i9 

25 

39794 

39967 

40140 

40312 

40483 

40654 

40824 

40993 

41162 

41330 

26 

41497 

41664 

41830 

41996 

42160 

42325 

42488 

42651 

42813 

42975 

27 

43136 

43297 

43457 

43616 

43775 

43933 

44091 

44248 

44404 

44560 

28 

44716 

44871 

45025 

45179 

45332 

45484 

45637 

45788 

45939 

46000 

29 

46240 

46389 

46538 

46687 

46835 

46982 

47129 

47276 

47422 

47567 

30 

47712 

47857 

48001 

48144 

48287 

48430 

48572 

48714 

48855 

48996 

31 

49136 

49276 

49415 

49554 

49693 

49831 

49969 

50106 

50243 

50379 

32 

50515 

50651 

50786 

50920 

51055 

5H89 

51322 

51455 

51587 

51720 

33 

5I85I 

51983 

52114 

52244 

52375 

52504 

52634 

52763 

52892 

53020 

34 

53148 

53275 

53403 

53529 

53656 

53782 

53908 

54033 

54158 

54283 

35 

54407 

54531 

54654 

54777 

54900 

55022 

55145 

55267 

55388 

55509 

36 

55630 

55751 

55871 

55991 

56110 

56229 

56348 

56467 

56585 

56703 

37 

56820 

56937 

57054 

57I7I 

57287 

57403 

57519 

57634 

57749 

57863 

38 

57978 

58093 

58206 

58320 

58433 

58546 

58659 

58771 

58883 

58995 

39 

59106 

59218 

59328 

59439 

59550 

59660 

59770 

59879 

59989 

60097 

40 

60206 

60314 

60423- 

60531 

60638 

60745 

60853 

60959 

61066 

61172 

41 

61278 

61384 

61490 

61595 

61700 

61805 

61009 

62014 

62118 

62221 

42 

62325 

62428 

62531 

62634 

62737 

62839 

62941 

63043 

63144 

63246 

43 

63347 

63448 

63548 

63649 

63749 

63849 

63949 

64048 

64147 

64246 

44 

64345 

64444 

64542 

64640 

64738 

64836 

64933 

65031 

65128 

65225 

8 

65321 
66276 

65418 
66370 

65514 
66464 

65609 
66558 

65706 
66652 

65801 
66745 

65896 
66839 

65992 
66932 

66087 
67025 

66181 
67117 

47 

67210 

67302 

67394 

67486 

67578 

67669 

67761 

67852 

67943 

68034 

48 

68124 

68215 

68305 

68395 

68485 

68574 

68664 

68753 

68842 

68931 

49 

69020 

69108 

69197 

69285 

69373 

69461 

69548 

69636 

69723 

69810 

50 

69897 

69984 

70070 

70157 

70243 

70329 

70415 

70501 

70586 

70672 

Si 

70757 

70842' 

70927 

71012 

71096 

71181 

71265 

71349 

71433 

7I5I7 

52 

71600 

71684 

71767 

71850 

71933 

72016 

72009 

72181 

72263 

72346 

53 

72428 

72509 

72591 

72673 

72754 

72835 

72916 

72997 

73078 

73159 

54 

73239 

73320 

73399 

73480 

7356o 

73639 

73719 

73799 

73fl8 

73957 

55 

74036 

74H5 

74194 

74273 

74351 

74429 

74507 

74586 

74663 

74741 

56 

74819 

74896 

74974 

75051 

75128 

75205 

75282 

75358 

75435 

755U 

57 

75587 

75664 

75740 

75815 

75891 

75967 

76042 

76118 

76193 

76268 

58 

76343 

76418 

76492 

76567 

76641 

76716 

76790 

76864 

76938 

77012 

59 

77085 

77159 

77232 

77305 

77379 

77452 

77525 

77597 

77670 

77743 

60 

77815 

77887 

7796o 

78032 

78104 

78176 

78247 

78319 

78390 

78462 

APPENDIX 


393 


TABLE  III. -LOGARITHMS  TO  BASE  10.  -  (Continued) 


No. 

0 

I 

2 

3 

4 

5 

6 

7 

8 

9 

61 

78533 

78604 

78675 

78746 

78817 

78888 

78958 

79029 

79099 

79169 

62 

79239 

79309 

79379 

79449 

79518 

79588 

79657 

79727 

79796 

79865 

63 

79934 

80003 

80072 

80140 

80209 

80277 

80346 

80414 

80482 

80550 

64 

80618 

80686 

80754 

80821 

80889 

80956 

81023 

81090 

81158 

81224 

65 

81291 

81358 

81425 

81491 

81558 

81624 

81690 

81757 

81823 

81889 

66 

81954 

82020 

82086 

82151 

82217 

82282 

82347 

82413 

82478 

82543 

67 

82607 

82672 

82737 

82802 

82866 

82930 

82995 

83059 

83123 

83187 

68 

83251 

83315 

83378 

83442 

83506 

83569 

83632 

83696 

83759 

83822 

69 

83885 

83948 

84011 

84073 

84136 

84198 

84261 

84323 

84386 

84448 

70 

84510 

84572 

84634 

84606 

84757 

84819 

84880 

84942 

85003 

85065 

71 

85126 

85187 

85248 

85309 

85370 

85431 

85491 

85552 

85612 

85673 

72 

85733 

85794 

85854 

85914 

85974 

86034 

86094 

86153 

86213 

86273 

73 

86332 

•86392 

86451 

86510 

86570 

86629 

86688 

86747 

86806 

80864 

74 

86923 

86982 

87040 

87099 

87157 

87216 

87274 

87332 

87390 

87448 

75 

87506 

87564 

87622 

87680 

87737 

87795 

87852 

87910 

87967 

88024 

76 

88081 

88138 

88196 

88252 

88309 

88366 

88423 

88480 

88536 

88593 

77 

88649 

88705 

88762 

88818 

88874 

88930 

88986 

89042 

89098 

89154 

78 

89209 

89265 

89321 

89376 

89432 

89487 

89542 

89597 

89653 

89708 

79 

89763 

89818 

89873 

80927 

89982 

00037 

90091 

90146 

90200 

00255 

80 

00309 

90363 

90417 

90472 

90526 

00580 

90634 

90687 

90741 

90795 

81 

90848 

90002 

90956 

91009 

91062 

91116 

91169 

91222 

91275 

91328 

82 

9I38I 

91434 

91487 

91540 

91593 

91645 

91698 

9I75I 

91803 

91855 

83 

91908 

91960 

92012 

92065 

92117 

92169 

92221 

92273 

92324 

92376 

84 

92428 

92480 

92531 

92583 

92634 

92686 

92737 

92789 

92840 

92891 

85 

92942 

92993 

93044 

93095 

93146 

93197 

93247 

93298 

93349 

93399 

86 

93450 

93500 

93551 

93601 

93651 

93702 

93752 

93802 

93852 

93902 

87 

93952 

94002 

94052 

94IOI 

94I5I 

94201 

94250 

94300 

94349 

94398 

88 

94448 

94498 

94547 

94596 

94645 

94694 

94743 

94791 

94841 

94890 

89 

94939 

94988 

95036 

95085 

95U4 

95182 

95231 

95279 

95328 

95376 

90 

95424 

95472 

95521 

95569 

95617 

95665 

95713 

95761 

95809 

95856 

91 

95904 

95952 

95999 

96047 

96095 

96142 

96190 

96237 

96284 

96332 

92 

96379 

96426 

96473 

96520 

96567 

96614 

96661 

96708 

06755 

96802 

93 

96848 

96895 

96942 

96988 

97035 

97081 

97128 

97174 

97220 

97267 

94 

97313 

97359 

97405 

97451 

97497 

97543 

97589 

97635 

97681 

97727 

95 

97772 

97818 

97864 

97909 

97955 

98000 

98046 

98091 

98137 

98182 

96 

98227 

98272 

98318 

98363 

98408 

98453 

98498 

98543 

98588 

98632 

97 

98677 

98722 

98767 

98811 

98856 

98900 

98945 

98089 

99034 

99078 

98 

99123 

99167 

9921  1 

99255 

99300 

99344 

99388 

99432 

09476 

99520 

99 

99564 

99607 

99651 

99695 

99739 

99782 

99826 

99870 

99913 

99957 

Characteristics  of  Logarithms: 
log  4030    =3.6053 
log   403    =2.6053 
log     40.3=1.6053 


log  4.03  =0.6053 
log  0.403  =1.6053 
log  0.0403  =2.6053 
log  0.00403  =3.  6053 


Useful  Constants: 


«  =  2.7182818 

IT  =  3.1415927 

i  radian  —  57.29578  degrees. 
i  degree  =    0.0174533  radian. 


394 


TELEGRAPH  ENGINEERING 


TABLE  IV.-HYBERBOLIC  FUNCTIONS 


M. 

sinh  u. 

cosh  «. 

«. 

sinh  w. 

cosh  «. 

«. 

sinh  «. 

coshw. 

o.oo 

0.0000 

I  .OOOO 

0.50 

0.5211 

I  .1276 

i  .00 

1.1752 

I-543I 

OI 

0100 

OOOI 

51 

5324 

1329 

05 

2539 

6038 

02 

O2OO 

OOO2 

52 

5438 

1383 

10 

3356 

6685 

03 

0300 

OOO5 

53 

5552 

1438 

15 

4208 

7374 

04 

O4OO 

.  0008 

54 

5666 

1494 

20 

5095 

8107 

05 

0500 

OOI3 

55 

5782 

1551 

25 

6019 

8884 

06 

O6OO 

OOl8 

56 

5897 

1609 

30 

6984 

1.9709 

07 

O7OI 

OO25 

57 

6014 

.1669 

35 

7991 

2-0583 

08 

080I 

0032 

58 

6131 

1730 

40 

1.9043 

1509 

09 

OQOI 

OO4I 

59 

6248 

1792 

45 

2.0143 

2488 

10 

1002 

0050 

60 

6367 

1855 

50 

1293 

3524 

II 

1  102 

006l 

61 

6485 

1919 

55 

2496 

4619 

12 

1203 

0072 

62 

6605 

1984 

60 

3756 

5775 

13 

1304 

0085 

63 

6725 

2051 

65 

5075 

f 

6995 

14 

1405 

0098 

64 

6846 

2119 

70 

6456 

8283 

IS 

1506 

OII3 

65 

6967 

2188 

75 

7904 

2.9642 

16 

1607 

OI28 

66 

7090 

2258 

80 

2.9422 

3.1075 

17 

I708 

0145 

67 

7213 

2330 

85 

3-IOI3 

2585 

18 

1810 

Ol62 

68 

7336 

2402 

90 

2682 

4177 

19 

1911 

0181 

69 

7461 

2476 

95 

4432 

5855 

20 

2013 

O2OI 

70 

7586 

2552 

2.00 

6269 

7622 

21 

2115 

O22I 

7i 

7712 

2628 

05 

3-8196 

3-9483 

22 

2218 

0243 

72 

7838 

2706 

10 

4.0219 

4-1443 

23 

2320 

0266 

73 

7966 

2785 

15 

2342 

3507 

24 

2423 

0289 

74 

8094 

2865 

20 

4571 

5679 

25 

2526 

03M 

75 

8223 

2947 

25 

6912 

4.7966 

26 

2629 

0340 

76 

8353 

3030 

30 

4-9370 

5-0372 

2? 

2733 

0367 

77 

8484 

3114 

35 

5.I95I 

2905 

28 

2837 

0395 

78 

8615 

3199 

40 

4662 

5569 

29 

2941 

0423 

79 

8748 

3286 

45 

5-7510 

5-8373 

30 

3045 

0453 

80 

8881 

3374 

50 

6.0502 

6.1323 

31 

3J5o 

0484 

81 

9015 

3464 

55 

3645 

4426 

32 

3255 

0516 

82 

9150 

3555 

60 

6.6947 

6  .  7690 

33 

336o 

0549 

83 

9286 

3647 

65 

7.0417 

7.1123 

34 

3466 

0584 

84 

9423 

3740 

70 

4063 

4735 

35 

3572 

0619 

85 

956i 

3835 

75 

7.7894 

7-8533 

36 

3678 

0655 

86 

9700 

3932 

80 

8.1919 

8.2527 

37 

3785 

0692 

87 

9840 

4029 

85 

8.6150 

8.6728 

38 

3892 

0731 

88 

0.9981 

4128 

90 

9.0596 

9.1146 

39 

4000 

0770 

89 

I.  0122 

4229 

95 

9.5268 

9-5791 

40 

4108 

0811 

90 

0265 

433i 

3-00 

10.0179 

10.0677 

4i 

4216 

0852 

9i 

0409 

4434 

05 

10.5340 

10.5814 

42 

4325 

0895 

92 

0554 

4539 

10 

11.0765 

11.1215 

43 

4434 

0939 

93 

0700 

4645 

15 

11.6466 

11.6895 

44 

4543 

0984 

94 

0847 

4753 

20 

12.2459 

12.2866 

45 

4653 

1030 

95 

0995 

4862 

25 

12.8758 

12.9146 

46 

4764 

1077 

96 

1144 

4973 

30 

13-5379 

13.5748 

47 

4875 

1125 

97 

1294 

5085 

35 

14-2338 

14.2689 

48 

4986 

"74 

98 

1446 

5199 

40 

14.9654 

14.9987 

49 

5098 

1225 

99 

1598 

5314 

45 

15-7343 

15.7661 

APPENDIX 


395 


TABLE  IV.  — HYPERBOLIC  FUNCTIONS.—  (Continued) 


«. 

sinh  «. 

cosh  M. 

u. 

sinh  u.       cosh  u. 

3.50 

16.5426 

16.5728 

6.00 

201.7132 

201.7156 

55 

I7-3923 

17.4210 

05 

212.0553 

212.0577 

60 

18.2855 

18.3128 

IO 

222.9278 

222.9300 

65 

19.2243 

19.2503 

15 

234.3576 

234.3598 

70 

20.2113 

20.2360 

20 

246.3735 

246.3755 

75 

21.2488 

21.2723 

25 

259.0054 

259.0074 

80 

22.3394 

22.3618 

30 

272.2850 

272.2869 

85 

23.5072 

35 

286.2455 

286.2472 

90 

24.6911 

24.7113 

40 

300.9217 

300.9233 

3-95 

25-958I 

25-9773 

45 

316.3504 

316.3520 

4.00 

27.2899 

27.3082 

So 

332.5700 

332.5716 

°5 

28  .  6900 

28.7074 

55 

349.6213 

349.6228 

IO 

30.1619 

30.1784 

60 

367.5469 

367.5483 

15 

31.7091 

31.7249 

65 

386.3915 

386.3928 

20 

33-3357 

33-3507 

70 

406  .  2023 

406.2035 

25 

35-0456 

35.0598 

75 

427.0287 

427.0300 

3° 

36-8431 

36.8567 

80 

448.9231 

448.9242 

35 

38.7328 

38.7457 

85 

471-9399 

471-9410 

40 

40.7193 

40.7316 

90 

496.1369 

496.1379 

45 

42.8076 

42.8193 

6-95 

521.5744 

521.5754 

50 

45.0030 

45.0141 

7.00 

548.3161 

548.3170 

55 

47.3109 

47-3215 

°5 

576.4289 

576.4298 

60 

49-7371 

49.7472 

IO 

605.9831 

605.9839 

65 

52.2877 

52.2973 

15 

637.0526 

637.0534 

70 

54.9690 

54.9781 

20 

669.7150 

669.7157 

75 

57.7878 

57.7965 

25 

704.0521 

704.0528 

80 

60.7511 

60.7593 

30 

740.1497 

740.1504 

85 

63.8663 

63.8741 

35 

778.0980 

778.0986 

90 

67.1412 

67.1486 

40 

817.9919 

817.9925 

4-95 

70.5839 

70.5910 

45 

859.93I3 

859.9318 

5-oo 

74.2032 

74.2099 

50 

904.0210 

904.0215 

05 

78.0080 

78.0144 

55 

950.37H 

950.3716 

10 

82.0079 

82.0140 

60 

999.0976 

999.0981 

IS 

86.2128 

86.2186 

65 

1050.323 

20 

90.6334 

90.6389 

70 

II04.I74 

25 

95-2805 

95.2858 

75 

1160.786 

30 

100.1659 

100.1709 

80 

1220.301 

35 

105.3018 

105.3065 

85 

1282.867 

40 

110.7009 

110.7055 

90 

1348.641 

45 

116.3769 

116.3812 

7-95 

1417.787 

5° 

122.3439 

122.3480 

8.00 

1490.479 

55 

128.6168 

128.6207 

05 

1566.698 

60 

135-2114 

135.2150 

10 

1647  .  234 

65 

142.1440 

142.1475 

IS 

1731.690 

70 

149.4320 

149-4354 

20 

1820.475 

75 

157-0938 

157.0969 

25 

I9I3.8I3 

80 

165.1482 

165.1513 

30 

2011.936 

85 

173.6158 

173.6186 

35 

2115.090 

90 

182.5173 

182.5201 

40 

2223.533 

95 

191.8754 

191.8780 

45 

2337-537 

INDEX 


Abbreviations  on  ticker  tapes,  121. 
used  in  telegraph  transmission,  28. 
Added  resistance  of  Field  quad.,  93. 
Admittance,  dielectric,  316. 
Advantage  of  double-current  duplex, 

74- 
using  two  generators  on  simplex 

lines,  342. 
Aerial  cables,  269. 

installation  of,  272. 
lines,  253. 

Alarm  indicators,  210. 
Alarms  of  fire,  transmission  of,  189. 

public,  200. 
Alphabets,  telegraph,  26,  121,  164, 

356. 
Alternating-current     track     relays, 

246. 
transmission  theory,  304. 

illustration  of,  330. 
Armor  on  cables,  380. 
Arresters,  lightning,  135,  260. 
Arrival  curves  on  cables,  353. 
Artificial  cables,  372. 
lines,  47,  51. 

calculation  of,  47,  62,  67,  71. 
Atkinson,  Richard  L.,  repeater,  40. 
Attenuation  coefficient,  311. 
Automatic  block  signals,  225. 
fire-alarm  repeaters,  206. 
repeaters,  37. 

retransmission  over  cables,  368. 
telegraphy,  108. 
transmitter,  no,  122. 


Auto-transformers     in     eliminating 

line  induction,  292. 
Ayrton,  Prof.  William  E.,  receiver 

resistance,  338. 

Balanced  circuit,  conditions  of,  52. 
Balancing  polar  duplex,  59. 

quadruplex,  93. 
Barclay,  John  C.,  printing  telegraph, 

121. 

Batteries,  location  on  lines,  6. 
primary,  20. 
secondary,  21. 

Baudot,  Jean  M.E.,  printer,  133, 163. 
Bell-striking  machines,  202. 
Block  signals,  automatic,  237. 
for  electric  roads,  231. 
for  steam  roads,  239. 
location  of  automatic,  232. 
manual  systems,  231. 
one-rail  system,  243. 
TDB  system,  235. 
two-rail  system,  244. 
types  of,  224. 

Bonding  of  cable  sheaths,  279. 
Bonds,  impedance  track,  244. 
Boxes,  cable  pole,  277. 
fire-alarm,  192. 
police  signal,  218. 
Bridge  duplex,  67. 

current  in  relay  of,  345. 
direct-point  repeater,  79. 
Wheatstone,  67,  373. 
Brooklyn  fire-alarm  system,  212. 


397 


398 


INDEX 


Brown,  Sidney  G.,  drum  relay,  368. 
Buckingham,  Charles  L.,  printer,  133. 
Bunnell  keys,  8. 
Burry,  John,  printing  telegraph,  133. 

Cable  keys,  363. 

letters,  382. 

service,  381. 

splices,  276. 

tariffs,  381. 

telegraphy,  theory  of,  347. 
Cables,  artificial,  372. 

attenuation  constant  of,  312. 

capacity  of,  287. 

constants  of  some,  381. 

design  of  submarine,  375. 

installation  of,  272. 

telegraph,  269. 
Capacity  of  cables,  287. 

line  wires,  284. 
Catlin,  Fred,  repeater,  42. 
Cells,  voltaic,  20. 
Central  stations,  fire-alarm,  202. 
Chapman,  Winthrop  M.,  block  sig- 
nals, 239. 
Characteristic    impedance    of    line, 

3r9- 

Cipher  messages,  151. 
Circuits  on  Northern  Pacific,  158. 
Clapp,  Martin  H.,  statistics,  158. 
Closed-circuit  Morse  system,  2,  5. 
Code,  Barclay  printing,  121. 

cable,  356. 

Continental,  25. 

Morse,  25. 

Murray  multiplex,  164. 

Phillips  punctuation,  25. 

words,  150. 

Cole,  Frederick  W.,  repeater,  206. 
Combination  fire-alarm  circuits,  212. 
Common-battery  telephone,  293. 


Composite  signalling,  296. 

railway,  298. 
Condensers  in  series  with  cables,  365. 

with  artificial  lines,  52. 
Conductance,  leakage,  287. 
Conductors,  constants  of,  262,  282. 
Conduit,  underground,  274. 
Continental  telegraph  code,  25,  356. 
Continuity-preserving     pole-chang- 
ers, 58. 

transmitters,  50. 
Copper-clad  wire,  29. 
inductance  of,  284. 

line  wire,  29,  262. 
Corrosion  of  cable  sheaths,  277. 
Cosines,  table  of,  388,  394. 
Crane,  Moses  G.,  fire-alarm  box,  194. 
Creed,  Frederick  G.,  printer,  133. 
Cr chore,  Dr.  Albert  C.,  cable  signal- 
ling,-3  74. 

duplex-diplex,  102. 
CR  Law,  364. 
Cross-arms,  pole,  259. 
Current  distribution  equations,  308. 
general,  329. 

in  duplex  circuits,  50,  62,  69,  75. 

in  leaky  lines,  334. 

propagation  over  lines,  303. 

ratio  in  quadruplex,  93. 

received  over  cable,  352. 

sources,  20. 

variation  in  quadruplex,  92. 

D'Arsonval,  Dr.  Arsene,  galvanome- 
ter, 360. 
Davis,  Minor  M.,  duplex,  63. 

quadruplex,  96. 
Day  letters,  152. 
Dean,  Robert  L.,  printer,  133. 
Deferred  cable  service,  381. 

overland  service,  152. 


INDEX 


399 


Delany,  Patrick  B.,  multiplex  tele- 
graph, 162. 

Desk,  police  central-office,  221. 
D'Humy,  Fernand  E.,  repeater,  42. 

reperforator,  114. 

Diehl,  Clark  £.,  relay  scheme,  95,  97. 
Dielectric  admittance,  316. 

permittivity,  286. 
Differential  duplex,  46. 

neutral  relay,  46. 

polarized  relay,  55. 
Diplex  signalling,  86. 
Direct-current  transmission  theory, 

305»  334- 

illustration  of,  338. 
point  repeaters,  76. 
Disk  railway  signals,  227. 
Distance  of  transmission  over  leaky 

lines,  32. 

over  perfectly-insulated  lines,  4. 
Distributing  frames,  143. 
Distributors,  synchronous,  164. 
Disturbances,  inductive,  288. 

elimination  of,  290. 
Dot-frequency,  304,  356. 
Double-block  condenser  scheme,  373. 

current  duplex,  74. 
Dry-core  cables,  269. 
Duplex  automatic  telegraphy,  113. 
balancing,  59. 

Barclay,  printing  telegraph,  126. 
bridge,  67. 

cable  telegraphy,  372. 
Davis  and  Eaves,  63. 
differential,  45. 
diplex  signalling,  102. 
double-current,  74. 
leak,  62. 
Morris,  66. 
polar,  56. 
improved,  63. 


Duplex,  Postal  Telegraph  Co.,  63. 

repeaters,  76. 

short-line,  66. 

signalling,  theory  of,  344. 

single-current,  46. 

Stearns,  46. 

switchboard  circuits,  142. 

telegraphy,  45. 

Western  Union  Co.,  71. 
Dwarf  railway  signals,  226. 

Earth  as  return  path,  i,  279. 

resistance,  280. 
Eaves,  Augustus  J.,  duplex,  63. 

quadruplex,  96. 
Economic  cable  determination,  376. 

span  lengths,  266. 
Edison,  Thomas  A.,  battery,  20,  22. 

quadruplex,  85. 

Electric  railways,  signals  for,  231, 
237,  242. 

telegraphy,  see  Telegraphy. 
Electrolysis  of  cable  sheaths,  277. 
Electromagnetic  induction,  288. 
Electrostatic  induction,  288. 
Equivalent  sine  curves,  304. 
Essick,  Samuel  V.,  printer,  133. 
Exponential  functions,  390. 

Faraday,  Prof.  Michael,  law  of,  278. 

polarizing  effect,  183. 
Fibre  stress  in  poles,  256. 
Field,  Stephen  D.,  key  system,  91. 
Fire-alarm  boxes,  192. 

central  stations,  202. 

devices  at  apparatus  houses,  210. 

repeaters,  206. 

systems,  operation  of,  212. 
statistics  of,  221. 

telegraphy,  189. 

transmitters,  203. 


4oo 


INDEX 


Fourier,  Jean  B.  /.,  series,  304,  348. 
Fournier,  Prof.,  television,  183. 
Fowle,  Frank  F. ,  copper-clad  wire,  2  84. 
Freir,  Samuel  P.,  neutral  relay,  96. 
Frequency,  dot-,  304,  356. 

reversal-,  356. 
Fuller,  John,  battery,  20. 
Fuses,  135. 

Galvanized  iron  wire,  29,  262. 

Gamewell,  John  N.,  fire-alarm  box, 
194. 

Gardiner,  James  M.,  fire-alarm  box, 
194. 

General  equations  of  line  current 
and  voltage,  329. 

Generators,  23. 

Ghegan,  John  /.,  repeater,  42. 

Gintl,  Dr.  Wilhelm,  duplex,  45. 

Gong  circuits,  fire-alarm,  211. 
electromechanical,  210. 

Gott,  John,  cable  signalling,  369. 

Gravity  battery,  20. 

Gray,  Prof.  Elisha,  telautograph,  170. 

Ground  as  return  path,  i,  279. 
connections,  281. 
resistance,  2,  280. 

Grounded  capacity  of  cables,  287. 

Growth  of  current  in  cables,  351. 
in  relay,  14,  35. 

Guild,    George   R.,    induction    tele- 
graph, 186. 

Guying  of  aerial  lines,  257. 

Half-set  repeaters,  80. 
Handling  of  telegraphic  traffic,  154. 
Hangers,  cable,  272. 
Hard-drawn  copper  wire,  29,  262. 
Heaviside,  Oliver,  earth  resistance, 

279. 
wire  capacity,  285. 


High-potential  leak  duplex,  62. 
Horton,  Lewis,  repeater,  42. 
Howler,  telephone,  300. 
Hughes,  Prof.  David  E.,  printer,  133. 
Hyperbolic  functions,  table  of,  394. 
use  of,  18,  265,  284,  322. 

Ideal  line,  velocity  of  wave  propaga- 
tion on,  313. 
Impedance  at  ends  of  line,  326. 

characteristic,  of  line,  319. 

conductor,  316. 

of  relays,  13. 

surge,  319,  357. 

track  bonds,  244. 
Indicators,  fire-alarm,  210. 
Inductance  of  line  wires,  283. 
Induction  repeaters,  187. 

telegraphs,  184. 
Inductive  line  interference,  288. 

shunt  for  recorders,  373. 
Installation  of  aerial  cables,  272. 
Instrument  tables,  145. 
Insulation  resistance  of  cables,  270, 

288,  379. 
of  lines,  30,  287. 
Insulators,  254. 
Interlacing  of  circuits,  194. 
Interlocking  machines,  247. 

plant  signals,  225,  247. 
Intermediate  offices,  6. 
Iron  line  wire,  29,  262. 

Jacks,  pin-,  139. 

spring-,  138. 
Joints  in  line  wire,  253. 
Joker  fire-alarm  circuits,  211. 

Kelvin,  Lord  (Wm.  Thomson),  CR 

law,  364.     *  C 
recorder,  360. 


INDEX 


401 


Kennelly,  Dr.  Arthur  E.,  hyperbolic 

functions,  321,  324. 
receiver  resistance,  357. 
Keyboard,  ticker,  119. 
Keys,  8,  363. 

Kinsley,  Carl,  printer,  133. 
Kirnan,  William  H.,  repeater,  206. 
Kleinschmidt,  Edward  E.,  perforator, 

122. 
Korn,  Dr.  Artur,  telephotography, 

175- 

Lalartde,  F.  de,  battery,  20. 
Leak  duplex,  62. 

relays,  78. 

resistance  of  Field  quad.,  93. 
Leakage,  line,  30. 
Leakance  of  lines,  287. 
Leclanche",  Georges,  battery,  20. 
Legibility  of  recorder  tapes,  359. 
Letters,  cable,  382. 

day  and  night,  152. 
Light-relay,  177. 

signals  on  railways,  225. 
Lightning  arresters,  135,  260. 
Lines,  aerial  open,  253. 

artificial,  47,  50. 

capacity  of,  284. 

inductance  of,  283. 

inductive  interference  on,  288. 

leakance  of,  287.  • 

resistance  of,  29,  283. 

telegraph,  28. 
Local  circuits,  4. 

duplex  and  quadruplex,  141. 
Locking  sheet,  250. 
Logarithms,  table  of,  392.    "• 
Loop  switchboards,  141. 
Low,  A.  M.,  television,  184. 
Lowy,   Heinrich,    earth    resistance, 


Maclaurin,  Colin,  series,  322. 
Magnet  bobbins,  windings  of,  13. 
Magneto  telephone  circuit,  293. 
Main  switchboards,  139. 
Malcolm,  Dr.  Henry  W.,  law,  364. 
Mallet  perforator,  109. 
Manholes,  275. 

Manual  block  signals,  224,  231. 
Marino,    Algeri,     telephotography, 

181. 

Marking  current,  112. 
Matthews,  W.  N.  and  Claude  L.,  con- 
duit costs,  274. 

Maver,  William,  Jr.,  repeater,  42. 
Mclntyre,  C.,  connector,  253. 
Mecograph  transmitting  key,  10. 
Mercadier,  Prof.  Ernest  J.  P.,  tele- 
graph system,  162. 
Messages,  telegraph,  types  of,  150. 
Messenger  wires,  272. 
Military  induction  telegraphs,  184. 
Milliken,  George  F.,  repeater,  42. 
Morkrum  printer  (Chas.  L.  Krum 

and  Jay  Morton),  133. 
Morris,  Robert  H.,  duplex,  66. 
Morse,  Prof.  Samuel  F.  B.,  code,  25. 

telegraph  system,  i. 
Motor-generator  sets,  24. 

switchboard  connections  of,  147. 
Muirhead,  Dr.  Alexander,  artificial 
cable,  372. 

relay,  368. 

Multiplex,    Murray,    page   printer, 
163. 

telegraphy,  162. 
Municipal  telegraphs,  189. 
Munier,    Claude    J.    A.,    printing 

telegraph,  133. 

Murray,  Donald,  printer,  133,  163. 
Mutual  capacity  of  wires,  285. 

inductance  of  wires,  283. 


402 


INDEX 


Neilson,  Hugh,  repeater,  42. 
Neomon,  interpretation  of,  316. 
Nernst,  Dr.  Wallher,  lamp,  177. 
Neutral  relays,  construction  of,  12. 

differential,  46. 

effect  of  current  reversals  in,  94. 

with  extra  coil,  96. 
Nicol,  William,  prism,  183. 
Night  letters,  152. 
Non-interfering  repeater,  206. 

signal  boxes,  194. 

Open-circuit  Morse  system,  5. 
Oscillogram  of  current  growth,  14. 
Overlap     railway     signal     system, 
233- 

Paper  winder,  16^  211. 
Patching  cords,  139. 
Peg-switch  panel,  136. 
Perforator,  keyboard,  122. 

Kleinschmidt,  122. 

mallet,  109. 

Permittivity  of  dielectric,  286. 
Phantom  telephone  circuit,  296. 
Phantoplex  system,  103. 
Phillips,    Walter    P.,    punctuation 
code,  25. 

repeater,  37,  80. 

Photographs,  transmission  of,  175. 
Physical  telephone  circuits,  296. 
Picard,  Pierre,  cable  signalling,  367. 

telegraph  system,  162. 
Pins,  insulator,  254. 
Plugs  for  pin  jacks,  139. 
Polar  direct-point  repeater,  76. 

duplex,  56. 
Polarized  block-signal  system,  240. 

relays,  53,  125. 

sounder,  186. 
Polar-neutral  track  relay,  240. 


Pole  boxes,  cable,  277. 
changer,  56. 

Western  Union,  72. 
spacing,  economic,  266. 
telegraph,  254. 
Police  patrol  boxes,  218. 
central  offices,  220. 
telegraphs,  217. 

statistics  of,  221. 

Pollak,   Dr.   Anloine,   writing   tele- 
graph, 167. 
Postal  polar  duplex,  63. 

quadruplex,  96. 
Power  switchboards,  146. 
Primary  batteries,  20. 
Printing  telegraph,  Barclay,  121. 

various,  mention  of,  133. 
Printing  telegraphy,  115. 
Problems,  43,  83,  106,  134,  161,  188, 

223,  251,  300,  346,  385. 
Propagation  constant  of  line,  318. 
Protective  devices,  135. 

resistances,  24,  6 1. 
Protectors,  145. 
Public  fire  alarms,  200. 

Quadrantal  operator,  316. 
Quadruplex,  Davis-Eaves,  96. 

Field  key  system,  91. 

Postal  Telegraph  Co.,  96. 

repeaters,  100. 

signalling,  theory  of,  344. 

switchboard  circuits,  141. 

systems,  operation  of,  87. 

telegraphy,  85. 

Western  Union,  98. 

Railway  composite  signalling,  298. 
interlocking  signals,  247. 
operation,  the  telegraph  in,  157. 
signal  systems,  224. 


INDEX 


403 


Receiver,  Barclay  printing,  126. 

Korn  telephotographic,  177. 

Pollak-Virag,  168. 

Receiving  instruments,  best  resist- 
ance of,  357. 
best  winding  for,  16. 
Recorder,  siphon,  360. 

Wheatstone,  108,  114. 
Reflection  coefficient,  320. 
Registers,  15,  210. 
Relay    current    in    bridge    duplex, 

345- 
Relays,  ampere-turns  for,  4. 

cable,  368. 

construction  of  neutral,  12. 

current  growth  in  neutral,  14. 

design  of,  35. 

Diehl  arrangement  of,  95,  97. 

differential  neutral,  46. 
polarized,  55,  125. 

leak,  78. 

light-,  177. 

phantoplex,  104. 

polarized,  53. 

resistance  of,  13,  19,  56. 

step-,  1 80. 

track,  240,  246. 

use  of,  3. 

windings,  16. 
Repeaters,  Atkinson,  40. 

closed-circuit,  37. 

direct-point,  76. 

duplex,  76. 

fire-alarm,  206. 

half-set,  80. 

induction,  187. 

open-circuit,  42. 

quadruplex,  100. 

simplex,  35. 
various,  mention  of,  42. 

Weiny-Phillips,  37,  '80. 


Repeating  coil,  294. 

sounders,  40,  67,  95. 
Reperforator,  114. 
Resistance  of  artificial  lines,  52. 

of  Field  quadruplex,  93. 

of  grounds,  2^2. 

of  polarized  relays,  56. 

of  relays,  13. 

of  selenium,  175. 

of  siphon  recorders,  362. 

of  sounders,  n. 

of  telegraph  lines,  29. 

of  the  earth,  279. 

of  wires,  283. 

Resonators  for  sounders,  n. 
Retardation  coils,  67. 

construction  of,  71. 
Retransmission  over  cables,  368. 
Reversal-frequency,  356. 
Rheostats,  artificial  line,  52. 
Rignoux,  television,  183. 
Ringing  over  composited  lines,  297. 
Rowland,  Prof.  Henry  .4. /printing 

telegraph,  133,  163. 
Riiddkk,  John  /.,  fire-alarm  box,  194. 
Ruhmer,  Ernst,  television,  183. 

Sags  of  wires,  262. 
Saturated-core  cables,  269. 
Secondary  batteries,  21. 
Sector  signal  boxes,  200. 
Seeing  at  a  distance,  183. 
Selenium  resistance  as  affected  by 

light,  175. 

Self-inductance  of  wires,  283. 
Semaphores,  225. 

operation  of,  229. 
Semi-automatic  transmitters,  10. 
Sextuplex  signalling,  104. 
Shading  coils  on  relay,  246. 
Shunt,  inductive,  373. 


404 


INDEX 


Side  circuit,  296. 

Siemens,  Dr.  E.  Werner,  printer,  133. 
Signal  boxes,  fire-alarm,  192. 
Gamewell  Company,  196. 
police,  218. 
successive,  195. 
Signalling  speed  on  cables,  363. 

types  of,  see  Telegraphy. 
Signals,  railway,  224. 
Silent  interval  in  cable  operation,  355. 
Simplex  instruments,  8. 

repeaters,  35. 

signalling  on  telephone  lines,  295. 
with  one  generator,  336. 
with  two  generators,  341. 

switchboard  circuit,  142. 

telegraphy,  i. 

Simultaneous  telegraphy  and  teleph- 
ony, 293. 

Sines,  table  of,  388,  394. 
Sine- wave  cable  signalling,  374. 
equivalent,  304. 

transmission,  illustration  of,  330. 
Single-current  duplex,  46. 

line  repeaters,  35. 

Morse  circuit,  2. 
Siphon  recorder,  360. 
Skelton,  Francis  A.,  repeater,  206. 
Sounders,  ampere-turns  for,  3. 

construction  of,  10. 

polarized,  186. 

repeating,  67,  95. 

resistance  of,  n. 

windings  of,  16. 
Spans,  economic  length  of,  266. 

wire,  261. 

Spark  quenching  at  contacts,  61,  73. 
Specific  inductive  capacity,  286. 
Speed,  effect  of  signalling,  334. 

of  cable  signalling,  363. 

of  signalling,  33. 


Splices,  cable,  276. 
Spring  jacks,  138. 

Squier,  Col.  George  0.,  cable  signal- 
ling, 374. 
Statistics  of  cables,  271,  381. 

of  telegraph  systems,  159. 
Steam  railways,  signals  for,  239. 
Stearns,  Joseph  B.,  duplex,  46. 
Steinheil,  Prof.  Karl  A.  von,  earth 

return,  279. 
Step-relay,  180. 
Storage  batteries,  21. 
Strap  and  disc  switch,  136. 
Stresses  in  poles,  256. 
Submarine  cables,  design  of,  375. 

telegraphy,  347. 
Successive  signal  boxes,  195. 
Sunflower  distributor,  126. 
Surge  impedance,  319,  357. 
Switchboards,  fire-alarm,  209. 

police  telegraph,  220. 

power,  146. 

telegraph,  138. 
Synchronous  distributors,  164. 

Tape,  perforated  transmitting,  108, 
122,  164,  167. 

siphon  recorder,  361. 

ticker,  120. 
Tariffs,  cable,  381. 

telegraph,  152. 
Taylor,  John  D.,  relay,  242. 
Telautograph,  170. 
Telegrams,  152. 
Telegraph  cables,  269. 

equation,  350. 

induction,  184. 

in  railway  operation,  157. 

lines,  253. 

current  propagation  in,  303. 

municipal,  189. 


INDEX 


405 


Telegraph  statistics,  159. 
Telegraphy,  automatic,  108. 

cable,  347. 

duplex,  45. 
cable,  372. 

fire-alarm,  189. 

multiplex,  162. 

police-patrol,  217. 

printing,  115. 

quadruplex,  85. 

simplex,  i. 

simultaneous  telephony  and,  293. 

submarine,  347. 

synchronous,  162. 

writing,  167. 
Telephone  circuits,  293. 
Telephoning  of  messages,  155. 
Telephony  on  telegraph  lines,  298. 

simultaneous  telegraphy  and,  293. 
Telephotography,  175. 

color,  181. 
Television,  182. 
Test  grounds,  282. 
Theory  of  current  propagation,  303. 
Thomson,  Prof.  Elihu,  arcs,  181. 
Ticker  telegraphs,  115. 
Tiffany,  George  S.,  telautograph,  170. 
Time  stamp,  automatic,  211. 
Timing  of  condenser  discharge,  52. 
Toye,  Benjamin  B.,  repeater,  42. 
Track  circuits,  239. 

relays,  240,  246. 
Traffic-direction-block  system,  235. 

telegraph,  150. 

handling  of,  154. 
Transformers,  use  of,  in  eliminating 

inductive  interference,  290. 
Transition  theory  of  transmission, 

305,  347- 

Transposition  insulator,  254. 
of  line  wires,  289. 


Transmission  distance  on  leaky  lines, 

32- 

on  perfectly-insulated  lines,  4. 
of  current  over  line,  303. 
of  signals  over  cables,  355. 
theory,  alternating-current,  306. 

direct-current,  334. 

transition,  305,  347. 
Transmitters,  automatic,  no,  122. 
continuity-preserving,  50,  58. 
fire-alarm,  203. 
Korn  telephotographic,  176. 
pole-changing,  56. 
Pollak-Virag,  167. 
repeater,  38,  40. 
semi-automatic,  10. 
ticker  telegraph,  115. 
Wheatstone,  108. 
Trigonometric  functions,  388. 

Underground  cables,  269. 

installation  of,  273. 
conduit,  274. 

Uniform  lines,  current  distribution 
on,  306. 

Van    Rysselberghe,    Prof.    Francois, 
composite  signalling,  296. 

Vector  representation,  315. 

Velocity  of  wave  propagation,  312. 

Vibrator,  siphon  recorder,  361. 

Vibroplex  transmitting  key,  10. 

Virag,  Josef,  writing  telegraphs,  167. 

Voltage  distribution  equations,  309. 

general,  329. 
on  cables,  350. 

Voltages,  standard,  in  telegraphy,  24. 

Wave-length  constant,  311. 

propagation,  theory  of,  306. 
Wedges  for  spring  jacks,  138. 


406 


INDEX 


Week-end  letters,  382. 
Weights  of  cable,  271,  380. 

sheaths,  380. 
of  line  wire,  29,  262. 
Weiny,  Roderick  H.,  repeater,  37, 

80. 

Western  Union  bridge-duplex,  71. 
quadruplex,  98. 
switchboards,  139. 
Wheatstone,  Sir  Charles,  automatic 

telegraph,  108. 
bridge,  67,  373. 

Whistle-blowing  machine,  200. 
Whitehead,  Charles  S.,  receiver  re- 
sistance, 338. 


Winding  constants  of  magnets,  13. 

for  receiving  instruments,  16. 
Wire,  bimetallic,  29. 

capacity  of  line,  284. 

leakance  of  line,  287. 

inductance  of  line,  283. 

resistance  of  line,  29,  283. 

sizes  of  line,  29. 

spans,  261. 

tensile  strength  of,  262. 

weights  of  line,  29,  262. 
Wright,  John  E.,  printer,  133. 
Writing  telegraphs,  167. 

Yorke,  George  M.,  line  induction,  292. 


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